dma-mapping: provide an interface to allocate IOVA

dma-mapping: provide an interface to allocate IOVA

Existing .map_page() callback provides two things at the same time:
allocates IOVA and links DMA pages. That combination works great for
most of the callers who use it in control paths, but less effective
in fast paths.

These advanced callers already manage their data in some sort of
database and can perform IOVA allocation in advance, leaving range
linkage operation to be in fast path.

Provide an interface to allocate/deallocate IOVA and next patch
link/unlink DMA ranges to that specific IOVA.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>