drm/amd/amdgpu: S4 issue for amdgpu (v2)

reset the asic if adapter is not powerdown when doing freeze()
thaw() and restore(), in order to get a valid state of adapter.

v2: squash in warning fix from Rex

Signed-off-by: JimQu <Jim.Qu@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Tested By: Shawn Starr <shawn.starr@rogers.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>