We are getting a dma-buf implementation completely separate from drm prime,
so rename the files now and cleanup the code a bit.

No functional change.
Signed-off-by: NChristian König <christian.koenig@amd.com>
Acked-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>