ARM: legoev3: update boot script to load uEnv.txt and .dtb

This updates the LEGO MINDSTORMS EV3 boot script to try loading a
uEnv.txt file and a da850-lego-ev3.dtb device tree during boot.

Signed-off-by: David Lechner <david@lechnology.com>

board/lego/ev3/README

@@ -9,14 +9,34 @@ Booting
 =======
 
 The EV3 contains a bootloader in EEPROM that loads u-boot.bin from address 0x0
-of the spi flash memory. Using the default configuration, u-boot will check to
-see if there is a boot.scr file on the first FAT partition of the mmc. If there
-is, it will run the script and boot the kernel from the uImage file also in
-the FAT partition. Otherwise, it will load a kernel and rootfs from the flash.
-The kernel must be stored at address 0x50000 on the flash and have a maximum
-size of 4MiB. The rootfs must be a squasfs image and stored at 0x450000 in the
-flash and have a maximum size of 10MiB. The flash starting at 0xE50000 is
-reserved for user data.
+of the SPI flash memory (with a size of 256KiB!). Because the EEPROM is read-
+only and it takes care of low level configuration (PLL and DDR), we don't use
+U-Boot to produce an SPL image.
+
+Using the default configuration, U-Boot had a boot scrips that works as follows:
+
+* Check to see if microSD card is present
+* If it is, try to load boot.scr from the first FAT partition
+* If loading boot.scr was successful, run it
+* Otherwise, try loading uEnv.txt
+* If loading uEnv.txt was successful, import it
+* If there is a uenvcmd variable (from uEnv.txt), run it
+* Try to load uImage from the first FAT partition
+* If it was successful, try to load da850-lego-ev3.dtb
+* If loading uImage was successful, boot it (DT is optional)
+* If none of the above was successful, try booting from flash
+
+Suggested Flash Memory Layout
+=============================
+
+The following is based on the default U-Boot configuration:
+
+| Image (file)       | Start Addr. | Max. Size         |
++--------------------+-------------+-------------------+
+| u-boot.bin         |         0x0 |  0x40000 (256KiB) |
+| da850-lego-ev3.dtb |     0x40000 |  0x10000 (64KiB)  |
+| uImage             |     0x50000 | 0x400000 (4MiB)   |
+| rootfs (squashfs)  |    0x450000 | 0xa00000 (10MiB)  |
 
 Writing image to flash
 ======================

include/configs/legoev3.h

@@ -84,34 +84,60 @@
 		"if run loadbootscr; then " \
 			"run bootscript; " \
 		"else " \
+			"if run loadbootenv; then " \
+				"echo Loaded env from ${bootenvfile};" \
+				"run importbootenv;" \
+			"fi;" \
+			"if test -n $uenvcmd; then " \
+				"echo Running uenvcmd...;" \
+				"run uenvcmd;" \
+			"fi;" \
 			"if run loadimage; then " \
 				"run mmcargs; " \
+				"if run loadfdt; then " \
+					"echo Using ${fdtfile}...;" \
+					"run fdtfixup; " \
+					"run fdtboot; "\
+				"fi; " \
 				"run mmcboot; " \
-			"else " \
-				"run flashargs; " \
-				"run flashboot; " \
 			"fi; " \
 		"fi; " \
-	"else " \
-		"run flashargs; " \
-		"run flashboot; " \
-	"fi"
+	"fi; "\
+	"run flashargs; " \
+	"run flashboot"
 #define CONFIG_EXTRA_ENV_SETTINGS \
+	"bootenvfile=uEnv.txt\0" \
+	"fdtfile=da850-lego-ev3.dtb\0" \
 	"memsize=64M\0" \
 	"filesyssize=10M\0" \
 	"verify=n\0" \
 	"console=ttyS1,115200n8\0" \
 	"bootscraddr=0xC0600000\0" \
+	"fdtaddr=0xC0600000\0" \
 	"loadaddr=0xC0007FC0\0" \
 	"filesysaddr=0xC1180000\0" \
 	"fwupdateboot=mw 0xFFFF1FFC 0x5555AAAA; reset\0" \
-	"mmcargs=setenv bootargs mem=${memsize} console=${console} root=/dev/mmcblk0p2 rw rootwait lpj=747520\0" \
+	"importbootenv=echo Importing environment...; " \
+		"env import -t ${loadaddr} ${filesize}\0" \
+	"loadbootenv=fatload mmc 0 ${loadaddr} ${bootenvfile}\0" \
+	"mmcargs=setenv bootargs console=${console} root=/dev/mmcblk0p2 rw " \
+		"rootwait ${optargs}\0" \
 	"mmcboot=bootm ${loadaddr}\0" \
-	"flashargs=setenv bootargs mem=${memsize} initrd=${filesysaddr},${filesyssize} root=/dev/ram0 rw rootfstype=squashfs console=${console} lpj=747520\0" \
-	"flashboot=sf probe 0; sf read ${loadaddr} 0x50000 0x400000; sf read ${filesysaddr} 0x450000 0xA00000; bootm ${loadaddr}\0" \
+	"flashargs=setenv bootargs initrd=${filesysaddr},${filesyssize} " \
+		"root=/dev/ram0 rw rootfstype=squashfs console=${console} " \
+		"${optargs}\0" \
+	"flashboot=sf probe 0; " \
+		"sf read ${fdtaddr} 0x40000 0x10000; " \
+		"sf read ${loadaddr} 0x50000 0x400000; " \
+		"sf read ${filesysaddr} 0x450000 0xA00000; " \
+		"run fdtfixup; " \
+		"run fdtboot\0" \
 	"loadimage=fatload mmc 0 ${loadaddr} uImage\0" \
+	"loadfdt=fatload mmc 0 ${fdtaddr} ${fdtfile}\0" \
+	"fdtfixup=fdt addr ${fdtaddr}; fdt resize; fdt chosen\0" \
+	"fdtboot=bootm ${loadaddr} - ${fdtaddr}\0" \
 	"loadbootscr=fatload mmc 0 ${bootscraddr} boot.scr\0" \
-	"bootscript=source ${bootscraddr}\0" \
+	"bootscript=source ${bootscraddr}\0"
 
 #ifdef CONFIG_CMD_BDI
 #define CONFIG_CLOCKS