iommu: SUN50I_IOMMU should depend on HAS_DMA

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+0x92e): undefined reference to `dma_pgprot'

IOMMU_DMA must not be selected, unless HAS_DMA=y.

Hence fix this by making SUN50I_IOMMU depend on HAS_DMA.

Fixes: 4100b8c2

 ("iommu: Add Allwinner H6 IOMMU driver")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20200629121146.24011-1-geert@linux-m68k.org
Signed-off-by: Joerg Roedel <jroedel@suse.de>