iommu/mediatek: Fix MTK_IOMMU dependencies

If NO_DMA=y (e.g. Sun-3 all{mod,yes}-config):

    drivers/iommu/dma-iommu.o: In function `iommu_dma_mmap':
    dma-iommu.c:(.text+0x836): undefined reference to `dma_pgprot'

IOMMU_DMA must not be selected, unless HAS_DMA=y.

Hence fix this by making MTK_IOMMU depend on HAS_DMA.
While at it, remove the dependency on ARM || ARM64, as that is already
implied by the dependency on ARCH_MEDIATEK.

Fixes: e93a1695

 ("iommu: Enable compile testing for some of drivers")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20200410143047.19691-1-geert@linux-m68k.org
Signed-off-by: Joerg Roedel <jroedel@suse.de>