imx8mn/8mp: Allow booting via USB

When trying to boot via USB on i.MX8MN it is necessary to specify
the U-Boot environment location, otherwise the boot process simply
hangs.

Specify the environment location when booting from USB.

Tested on a imx8mn-evk.

Suggested-by: Michael Nazzareno Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Fabio Estevam <festevam@denx.de>
Tested-By: Tim Harvey <tharvey@gateworks.com>
diff --git a/arch/arm/mach-imx/imx8m/soc.c b/arch/arm/mach-imx/imx8m/soc.c
index 8e23e6d..bc3379a 100644
--- a/arch/arm/mach-imx/imx8m/soc.c
+++ b/arch/arm/mach-imx/imx8m/soc.c
@@ -1535,6 +1535,16 @@
 		return ENVL_UNKNOWN;
 
 	switch (dev) {
+	case USB_BOOT:
+		if (IS_ENABLED(CONFIG_ENV_IS_IN_SPI_FLASH))
+			return ENVL_SPI_FLASH;
+		if (IS_ENABLED(CONFIG_ENV_IS_IN_NAND))
+			return ENVL_NAND;
+		if (IS_ENABLED(CONFIG_ENV_IS_IN_MMC))
+			return ENVL_MMC;
+		if (IS_ENABLED(CONFIG_ENV_IS_NOWHERE))
+			return ENVL_NOWHERE;
+		return ENVL_UNKNOWN;
 	case QSPI_BOOT:
 	case SPI_NOR_BOOT:
 		if (IS_ENABLED(CONFIG_ENV_IS_IN_SPI_FLASH))