iommu/mediatek: Remove bogus 'select' statements

The mediatek IOMMU driver enables some drivers that it does not directly
rely on, and that causes a warning for build testing:

warning: (MTK_IOMMU_V1) selects COMMON_CLK_MT2701_VDECSYS which has unmet direct dependencies (COMMON_CLK && COMMON_CLK_MT2701)
warning: (MTK_IOMMU_V1) selects COMMON_CLK_MT2701_IMGSYS which has unmet direct dependencies (COMMON_CLK && COMMON_CLK_MT2701)
warning: (MTK_IOMMU_V1) selects COMMON_CLK_MT2701_MMSYS which has unmet direct dependencies (COMMON_CLK && COMMON_CLK_MT2701)

This removes the select statements.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>