dma_map_resource() and dma_unmap_resource() functions are used to map
and unmap of memory-mapped IO resources so they can be accessed by
the device.
Required by drm-kmod v5.5 to be built.
While for drm-kmod 6.6-lts only amdgpu uses these in one place and
the code apparently has not been exercised a lot it has been around
like this for years. With changing the underlying implementations
bring it into the tree; should we find errors with it they can also
be fixed here.
Obtained from: D30933 (by wulf)
Sponsored by: The FreeBSD Foundation
MFC after: 3 days