drm/amdgpu: enable gfx clock gating for rn

Enable gfx cg/mg/cp etc clock gating.

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