am335x_evm: Allow booting from usb-storage device

Signed-off-by: Matwey V. Kornilov <matwey.kornilov@gmail.com>
diff --git a/include/configs/am335x_evm.h b/include/configs/am335x_evm.h
index 9c4ef36..103c046 100644
--- a/include/configs/am335x_evm.h
+++ b/include/configs/am335x_evm.h
@@ -66,6 +66,12 @@
 #define BOOTENV_DEV_NAME_NAND(devtypeu, devtypel, instance) \
 	#devtypel #instance " "
 
+#if CONFIG_IS_ENABLED(CMD_USB)
+# define BOOT_TARGET_USB(func) func(USB, usb, 0)
+#else
+# define BOOT_TARGET_USB(func)
+#endif
+
 #if CONFIG_IS_ENABLED(CMD_PXE)
 # define BOOT_TARGET_PXE(func) func(PXE, pxe, na)
 #else
@@ -84,6 +90,7 @@
 	func(MMC, mmc, 1) \
 	func(LEGACY_MMC, legacy_mmc, 1) \
 	func(NAND, nand, 0) \
+	BOOT_TARGET_USB(func) \
 	BOOT_TARGET_PXE(func) \
 	BOOT_TARGET_DHCP(func)