ARM: rpi: support an environment

Enable ENV_IS_IN_FAT so that the environment can be stored persistently.
It's stored in the FAT partition that the RPi firmware requires. On most
RPis, this is on the SD card (which must be present in order for the
system to boot). On the CM this is on the built-in eMMC device.

Since we now have a persistent environment, there's no need to load
uEnv.txt at boot; we only did that to work around the lack of persistent
environment.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>

include/configs/rpi.h

@@ -105,15 +105,15 @@
 
 /* Environment */
 #define CONFIG_ENV_SIZE			SZ_16K
-#define CONFIG_ENV_IS_NOWHERE
+#define CONFIG_ENV_IS_IN_FAT
+#define FAT_ENV_INTERFACE		"mmc"
+#define FAT_ENV_DEVICE_AND_PART		"0:1"
+#define FAT_ENV_FILE			"uboot.env"
+#define CONFIG_FAT_WRITE
 #define CONFIG_ENV_VARS_UBOOT_CONFIG
 #define CONFIG_SYS_LOAD_ADDR		0x1000000
 #define CONFIG_CONSOLE_MUX
 #define CONFIG_SYS_CONSOLE_IS_IN_ENV
-#define CONFIG_PREBOOT \
-	"if load mmc 0:1 ${loadaddr} /uEnv.txt; then " \
-		"env import -t -r ${loadaddr} ${filesize}; " \
-	"fi"
 
 /* Shell */
 #define CONFIG_SYS_MAXARGS		8
@@ -138,7 +138,6 @@
 
 /* Some things don't make sense on this HW or yet */
 #undef CONFIG_CMD_FPGA
-#undef CONFIG_CMD_SAVEENV
 
 /* Environment */
 #define ENV_DEVICE_SETTINGS \