drm/amdgpu: fix the hw hang during perform system reboot and reset

The system reboot failed as some IP blocks enter power gate before perform
hw resource destory. Meanwhile use unify interface to set device CGPG to ungate
state can simplify the amdgpu poweroff or reset ungate guard.

Fixes: 487eca11 ("drm/amdgpu: fix gfx hang during suspend with video playback (v2)")
Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Tested-by: Mengbing Wang <Mengbing.Wang@amd.com>
Tested-by: Paul Menzel <pmenzel@molgen.mpg.de>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>