drm/amdgpu: add atpx quirk handling (v2)

Add quirks for handling PX/HG systems.  In this case, add
a quirk for a weston dGPU that only seems to properly power
down using ATPX power control rather than HG (_PR3).

v2: append a new weston XT

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Junwei Zhang <Jerry.Zhang@amd.com> (v2)
Reviewed-and-Tested-by: Junwei Zhang <Jerry.Zhang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Cc: stable@vger.kernel.org