drm/radeon: implement blit copy callback for CIK

Uses the CP ring rather than the DMA ring.  Useful
for debugging and benchmarking.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --cc drivers/gpu/drm/radeon/cik.c
Simple merge

diff --cc drivers/gpu/drm/radeon/cikd.h
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_asic.h
Simple merge