remove hwsw_dma_ops

This removes remove hwsw_dma_ops (and hwsw_*
functions). hwsw_dma_get_ops can select swiotlb_dma_ops and
sba_dma_ops appropriately.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>