ARM: embestmx6boards: convert the mars/riot boards to DM_MMC

Convert the two Embest boards to use DM MMC.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Cc: "Eric BĂ©nard" <eric@eukrea.com>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
diff --git a/configs/marsboard_defconfig b/configs/marsboard_defconfig
index 4d15f04..63fc60a 100644
--- a/configs/marsboard_defconfig
+++ b/configs/marsboard_defconfig
@@ -30,6 +30,7 @@
 CONFIG_DM=y
 CONFIG_DM_GPIO=y
 CONFIG_BOUNCE_BUFFER=y
+CONFIG_DM_MMC=y
 CONFIG_FSL_USDHC=y
 CONFIG_PINCTRL=y
 CONFIG_PINCTRL_IMX6=y