am335x_evm: Rework bootcmd to handle two MMC devs

The BeagleBone Black can boot from either the MMC card
or eMMC chip on board. We should try both interfaces.

This modification also allows a graceful fallback if
a device exists but boot images are not present on it.

Changes for v2:

* Fix boot partition - it should always show up as mmcblk0p2
* Fix missing FDT load
Signed-off-by: NJustin Waters <justin.waters@timesys.com>

include/configs/am335x_evm.h

@@ -131,9 +131,23 @@
 	"loadramdisk=load mmc ${mmcdev} ${rdaddr} ramdisk.gz\0" \
 	"loaduimage=load mmc ${bootpart} ${loadaddr} ${bootdir}/${bootfile}\0" \
 	"loadfdt=load mmc ${bootpart} ${fdtaddr} ${bootdir}/${fdtfile}\0" \
-	"mmcboot=echo Booting from mmc ...; " \
-		"run mmcargs; " \
-		"bootm ${loadaddr} - ${fdtaddr}\0" \
+	"mmcboot=mmc dev ${mmcdev}; " \
+		"if mmc rescan; then " \
+			"echo SD/MMC found on device ${mmcdev};" \
+			"if run loadbootenv; then " \
+				"echo Loaded environment from ${bootenv};" \
+				"run importbootenv;" \
+			"fi;" \
+			"if test -n $uenvcmd; then " \
+				"echo Running uenvcmd ...;" \
+				"run uenvcmd;" \
+			"fi;" \
+			"if run loaduimage; then " \
+				"run loadfdt;" \
+				"run mmcargs; " \
+				"bootm ${loadaddr} - ${fdtaddr};" \
+			"fi;" \
+		"fi;\0" \
 	"spiboot=echo Booting from spi ...; " \
 		"run spiargs; " \
 		"sf probe ${spibusno}:0; " \
@@ -165,23 +179,11 @@
 
 #define CONFIG_BOOTCOMMAND \
 	"run findfdt; " \
-	"mmc dev ${mmcdev}; if mmc rescan; then " \
-		"echo SD/MMC found on device ${mmcdev};" \
-		"if run loadbootenv; then " \
-			"echo Loaded environment from ${bootenv};" \
-			"run importbootenv;" \
-		"fi;" \
-		"if test -n $uenvcmd; then " \
-			"echo Running uenvcmd ...;" \
-			"run uenvcmd;" \
-		"fi;" \
-		"if run loaduimage; then " \
-			"run loadfdt;" \
-			"run mmcboot;" \
-		"fi;" \
-	"else " \
-		"run nandboot;" \
-	"fi;" \
+	"run mmcboot;" \
+	"setenv mmcdev 1; " \
+	"setenv bootpart 1:2; " \
+	"run mmcboot;" \
+	"run nandboot;"
 
 /* Clock Defines */
 #define V_OSCK				24000000  /* Clock output from T2 */