imx: nitrogen6x: Make use of both uSD and SD slots to load script or kernel on Sabrelite board

Sabrelite board has two solts: 0 is SD3 (bottom) slot and 1 is uSD4 (top) slot.
This patch makes use of both slots instead of only one.

Signed-off-by: Guillaume GARDET <guillaume.gardet@free.fr>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Eric Nelson <eric.nelson@boundarydevices.com>
Reviewed-by: Eric Nelson <eric.nelson@boundarydevices.com>
Acked-by: Eric Nelson <eric.nelson@boundarydevices.com>
Reviewed-by: Eric Nelson <eric.nelson@boundarydevices.com>
Acked-by: Eric Nelson <eric.nelson@boundarydevices.com>

include/configs/nitrogen6x.h

@@ -186,7 +186,7 @@
 	"fdt_addr=0x18000000\0" \
 	"boot_fdt=try\0" \
 	"ip_dyn=yes\0" \
-	"mmcdev=0\0" \
+	"mmcdevs=0 1\0" \
 	"mmcpart=1\0" \
 	"mmcroot=/dev/mmcblk0p2 rootwait rw\0" \
 	"mmcargs=setenv bootargs console=${console},${baudrate} " \
@@ -238,16 +238,19 @@
 		"fi;\0"
 
 #define CONFIG_BOOTCOMMAND \
-	   "mmc dev ${mmcdev}; if mmc rescan; then " \
-		   "if run loadbootscript; then " \
-			   "run bootscript; " \
-		   "else " \
-			   "if run loaduimage; then " \
-				   "run mmcboot; " \
-			   "else run netboot; " \
-			   "fi; " \
-		   "fi; " \
-	   "else run netboot; fi"
+	"for mmcdev in ${mmcdevs}; do " \
+		"mmc dev ${mmcdev}; " \
+		"if mmc rescan; then " \
+			"if run loadbootscript; then " \
+				"run bootscript; " \
+			"else " \
+				"if run loaduimage; then " \
+					"run mmcboot; " \
+				"fi; " \
+			"fi; " \
+		"fi; " \
+	"done; " \
+	"run netboot; "
 #else
 #define CONFIG_EXTRA_ENV_SETTINGS \
 	"console=ttymxc1\0" \