arm64: Combine coherent and non-coherent swiotlb dma_ops

Since dev_archdata now has a dma_coherent state, combine the two
coherent and non-coherent operations and remove their declaration,
together with set_dma_ops, from the arch dma-mapping.h file.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>