x86/dma: Use generic swiotlb_ops

The generic swiotlb DMA ops were based on the x86 ones and provide
equivalent functionality, so use them.

Also fix the sta2x11 case.  For that SOC the DMA map ops need an
additional physical to DMA address translations.  For swiotlb buffers
that is done throught the phys_to_dma helper, but the sta2x11_dma_ops
also added an additional translation on the return value from
x86_swiotlb_alloc_coherent, which is only correct if that functions
returns a direct allocation and not a swiotlb buffer.  With the
generic swiotlb and DMA-direct code phys_to_dma is not always used
and the separate sta2x11_dma_ops can be replaced with a simple
bit that marks if the additional physical to DMA address translation
is needed.

Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Jon Mason <jdmason@kudzu.us>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Muli Ben-Yehuda <mulix@mulix.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: iommu@lists.linux-foundation.org
Link: http://lkml.kernel.org/r/20180319103826.12853-5-hch@lst.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>