uboot-imx

arm: socfpga: Enable DFU MMC support only if DM_MMC is enabled

It is not possible to compile DFU MMC support if the MMC support is not
compiled into U-Boot. Secure the code with an ifdef to prevent compiler
splat.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>
Cc: Chin Liang See <clsee@altera.com>