Convert CONFIG_CMD_MMC to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_MMC

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/s32v234evb_defconfig b/configs/s32v234evb_defconfig
index 99720a9..78450c2 100644
--- a/configs/s32v234evb_defconfig
+++ b/configs/s32v234evb_defconfig
@@ -13,6 +13,7 @@
 CONFIG_CMD_MEMTEST=y
 CONFIG_SYS_MEMTEST_START=0xc0000000
 CONFIG_SYS_MEMTEST_END=0xc7c00000
+CONFIG_CMD_MMC=y
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_DM=y