board: ge: bx50v3: Enable CONFIG_DM_MMC

Use MMC device model, and remove USDHC pin configuration code since the
pinctrl driver is used.

Signed-off-by: Ian Ray <ian.ray@ge.com>
diff --git a/configs/ge_bx50v3_defconfig b/configs/ge_bx50v3_defconfig
index a883f65..b0f5c1f 100644
--- a/configs/ge_bx50v3_defconfig
+++ b/configs/ge_bx50v3_defconfig
@@ -54,3 +54,7 @@
 CONFIG_CMD_DM=y
 CONFIG_OF_CONTROL=y
 CONFIG_DEFAULT_DEVICE_TREE="imx6q-bx50v3"
+CONFIG_DM_MMC=y
+CONFIG_BLK=y
+CONFIG_PINCTRL=y
+CONFIG_PINCTRL_IMX6=y