iommu/mediatek: Select ARM_DMA_USE_IOMMU

iommu/mediatek: Select ARM_DMA_USE_IOMMU

The newly added Mediatek IOMMU driver uses the IOMMU_DMA infrastructure,
but unlike other such drivers, it does not select 'ARM_DMA_USE_IOMMU',
which is a prerequisite, leading to a link error:

warning: (MTK_IOMMU) selects IOMMU_DMA which has unmet direct dependencies (IOMMU_SUPPORT && NEED_SG_DMA_LENGTH)
drivers/iommu/built-in.o: In function `iommu_put_dma_cookie':
mtk_iommu.c:(.text+0x11fe): undefined reference to `put_iova_domain'
drivers/iommu/built-in.o: In function `iommu_dma_init_domain':
mtk_iommu.c:(.text+0x1316): undefined reference to `init_iova_domain'
drivers/iommu/built-in.o: In function `__iommu_dma_unmap':
mtk_iommu.c:(.text+0x1380): undefined reference to `find_iova'

This adds the same select that the other drivers have. On a related
note, I wonder if we should just always select ARM_DMA_USE_IOMMU
whenever any IOMMU driver is enabled. Are there any cases where
we would enable an IOMMU but not use it?

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 0df4fabe208d ("iommu/mediatek: Add mt8173 IOMMU driver")
Signed-off-by: Joerg Roedel <jroedel@suse.de>