ANDROID: iommu/dma: Add support fo DMA_ATTR_SYS_CACHE_ONLY

IOMMU_SYS_CACHE_ONLY allows buffers for non-coherent devices
to be mapped with the correct memory attributes so that the buffers
can be cached in the system cache. However, this property
is only usable by drivers that invoke the IOMMU API directly;
it is not usable by drivers that use the DMA API.

Thus, introduce DMA_ATTR_SYS_CACHE_ONLY, so that drivers for
non-coherent devices that use the DMA API can use it to specify if
they want a buffer to be cached in the system cache.

Bug: 176778547
Change-Id: I849d7a3f36b689afd2f6ee400507223fd6395158
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>