drm/amdgpu: add kiq version interface for RREG32/WREG32

Reading some registers by mmio will result in hang when GPU is in
"gfxoff" state.This problem can be solved by GPU in "ring command
packages" way.

Signed-off-by: chen gong <curry.gong@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>