drm/amdgpu: move full access into amdgpu_device_ip_suspend

It will be more safe to make full-acess include both phase1 and phase2.
Then accessing special registeris wherever at phase1 or phase2 will not
block any shutdown and suspend process under virtualization.

Signed-off-by: Yintian Tao <yttao@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>