arc: emsdp/iotdk: Switch to DM_MMC

Somehow EMSDP & IoT DK boards were skipped on ARC boads conversion
to DM MMC. So doing it now.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
diff --git a/configs/iot_devkit_defconfig b/configs/iot_devkit_defconfig
index 24bbe3f..42278d4 100644
--- a/configs/iot_devkit_defconfig
+++ b/configs/iot_devkit_defconfig
@@ -29,7 +29,9 @@
 # CONFIG_NET is not set
 CONFIG_DM=y
 CONFIG_MMC=y
+CONFIG_DM_MMC=y
 CONFIG_MMC_DW=y
+CONFIG_MMC_DW_SNPS=y
 CONFIG_DM_SERIAL=y
 CONFIG_SYS_NS16550=y
 CONFIG_USB=y