configs: imx6sabreauto: Add DM_MMC support

Add DM_MMC config to imx6sabreauto defconfig.

Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
diff --git a/configs/mx6sabreauto_defconfig b/configs/mx6sabreauto_defconfig
index cc53b93..61d830c 100644
--- a/configs/mx6sabreauto_defconfig
+++ b/configs/mx6sabreauto_defconfig
@@ -44,6 +44,7 @@
 CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
 CONFIG_DFU_MMC=y
 CONFIG_DFU_SF=y
+CONFIG_DM_MMC=y
 CONFIG_FSL_ESDHC=y
 CONFIG_NAND=y
 CONFIG_NAND_MXS=y