drm/radeon: plug in blit copy routine for SI

Uses CP DMA packet just like previous asics.
Useful for debugging and benchmarking.  Uses
same packet format as prior asics.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_asic.c

@@ -1879,7 +1879,7 @@ static struct radeon_asic si_asic = {
 		.hdmi_setmode = &evergreen_hdmi_setmode,
 	},
 	.copy = {
-		.blit = NULL,
+		.blit = &r600_copy_cpdma,
 		.blit_ring_index = RADEON_RING_TYPE_GFX_INDEX,
 		.dma = &si_copy_dma,
 		.dma_ring_index = R600_RING_TYPE_DMA_INDEX,