pico-imx6ul, pico-imx7d: Enable USB and PXE boot support

This allow the use of a USB storage or PXE network booting as
fallback, allowing for example for manufacturing installation of eMMC
storage in an easy way.

Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
diff --git a/include/configs/pico-imx6ul.h b/include/configs/pico-imx6ul.h
index 0fea2d6..8082b74 100644
--- a/include/configs/pico-imx6ul.h
+++ b/include/configs/pico-imx6ul.h
@@ -103,6 +103,8 @@
 
 #define BOOT_TARGET_DEVICES(func) \
 	func(MMC, mmc, 0) \
+	func(USB, usb, 0) \
+	func(PXE, pxe, na) \
 	func(DHCP, dhcp, na)
 
 #include <config_distro_bootcmd.h>