drm/radeon: implement clock and power gating for CIK (v3)

Only the APUs support power gating.

v2: disable cgcg for now
v3: workaround hw issue in mgcg

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/radeon/si.c b/drivers/gpu/drm/radeon/si.c
index 8b8963d..4f91e1f 100644
--- a/drivers/gpu/drm/radeon/si.c
+++ b/drivers/gpu/drm/radeon/si.c
@@ -4901,7 +4901,7 @@
 	WREG32_UVD_CTX(UVD_CGC_CTRL2, tmp2);
 }
 
-static void si_init_uvd_internal_cg(struct radeon_device *rdev)
+void si_init_uvd_internal_cg(struct radeon_device *rdev)
 {
 	bool hw_mode = true;