drm/amdgpu: re-enable suspend phase 2 for S0ix

This really needs to be done to properly tear down
the device.  SMC, PSP, and GFX are still problematic,
need to dig deeper into what aspect of them that is
problematic.

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