drm/amdgpu/swsmu: skip gfx cgpg on s0ix suspend

The SMU expects CGPG to be enabled when entering S0ix.
with this we can re-enable SMU suspend.

Acked-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>