imx: kontron-sl-mx8mm: Enable environment in MMC

In case we boot from SD card or eMMC, we also want to load
the environment from the according boot device.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Fabio Estevam <festevam@denx.de>
diff --git a/configs/kontron-sl-mx8mm_defconfig b/configs/kontron-sl-mx8mm_defconfig
index e796189..18b926e 100644
--- a/configs/kontron-sl-mx8mm_defconfig
+++ b/configs/kontron-sl-mx8mm_defconfig
@@ -71,6 +71,7 @@
 CONFIG_CMD_EXT4_WRITE=y
 CONFIG_OF_CONTROL=y
 CONFIG_SPL_OF_CONTROL=y
+CONFIG_ENV_IS_IN_MMC=y
 CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y