[media] drivers/media/platform/Kconfig: fix VIDEO_MEDIATEK_VCODEC dependency

Allow VIDEO_MEDIATEK_VCODEC to build when COMPILE_TEST is set (even
without MTK_IOMMU).

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>