drm/amdgpu: disable MMHUB power gating on raven

MMHUB power gating still has issue, and doesn't work on raven at current. So
disable it for the moment.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Acked-by: Hawking Zhang <Hawking.Zhang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/amd/amdgpu/soc15.c

@@ -666,8 +666,8 @@ static int soc15_common_early_init(void *handle)
 			AMD_CG_SUPPORT_MC_LS |
 			AMD_CG_SUPPORT_SDMA_MGCG |
 			AMD_CG_SUPPORT_SDMA_LS;
-		adev->pg_flags = AMD_PG_SUPPORT_SDMA |
-				 AMD_PG_SUPPORT_MMHUB;
+		adev->pg_flags = AMD_PG_SUPPORT_SDMA;
+
 		adev->external_rev_id = 0x1;
 		break;
 	default: