configs: transformer_t30: support booting from USB

Change boot logic to primary try to boot from USB in dock, then
from microSD and lastly from eMMC.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
diff --git a/configs/tf600t.config b/configs/tf600t.config
index 89d8db4..18ab4fb 100644
--- a/configs/tf600t.config
+++ b/configs/tf600t.config
@@ -1,4 +1,4 @@
 CONFIG_DEFAULT_DEVICE_TREE="tegra30-asus-tf600t"
 CONFIG_TRANSFORMER_SPI_BOOT=y
-CONFIG_BOOTCOMMAND="setenv gpio_button 222; if run check_button; then poweroff; fi; setenv gpio_button 132; if run check_button; then echo Starting SPI flash update ...; run update_spi; fi; run bootcmd_mmc1; run bootcmd_mmc0; poweroff;"
+CONFIG_BOOTCOMMAND="setenv gpio_button 222; if run check_button; then poweroff; fi; setenv gpio_button 132; if run check_button; then echo Starting SPI flash update ...; run update_spi; fi; run bootcmd_usb0; run bootcmd_mmc1; run bootcmd_mmc0; poweroff;"
 CONFIG_USB_GADGET_PRODUCT_NUM=0x4d00
diff --git a/configs/transformer_t30_defconfig b/configs/transformer_t30_defconfig
index 8e03a60..8fbf231 100644
--- a/configs/transformer_t30_defconfig
+++ b/configs/transformer_t30_defconfig
@@ -20,7 +20,7 @@
 CONFIG_AUTOBOOT_KEYED_CTRLC=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_OF_SYSTEM_SETUP=y
-CONFIG_BOOTCOMMAND="setenv gpio_button 150; if run check_button; then poweroff; fi; setenv gpio_button 131; if run check_button; then bootmenu; fi; run bootcmd_mmc1; run bootcmd_mmc0; poweroff;"
+CONFIG_BOOTCOMMAND="setenv gpio_button 150; if run check_button; then poweroff; fi; setenv gpio_button 131; if run check_button; then bootmenu; fi; run bootcmd_usb0; run bootcmd_mmc1; run bootcmd_mmc0; poweroff;"
 CONFIG_SPL_FOOTPRINT_LIMIT=y
 CONFIG_SPL_MAX_FOOTPRINT=0x8000
 # CONFIG_SPL_SHARES_INIT_SP_ADDR is not set