ARM: multi_v7_defconfig: Enable Exynos MFC driver as module

Exynos SoCs have a Multi Format Video Hardware Codec (MFC) IP block that
can be used to {en,de}code video streams by hardware. Enable support for
its driver as a module so the MFC can be tested.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>