drm/amdgpu: add GFX_PIPELINE capacity check for updating gfx cgpg

Before disable gfx pipeline power gating need check the flag AMD_PG_SUPPORT_GFX_PIPELINE.

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