drm/amdgpu: clean up the suspend_complete

To check the status of S3 suspend completion,
use the PM core pm_suspend_global_flags bit(1)
to detect S3 abort events. Therefore, clean up
the AMDGPU driver's private flag suspend_complete.

Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>