drm/amdgpu: request/release full gpu access if device is vf

For gpu vf device, first need to request full gpu access before
accessing gpu registers, and release full gpu access after the
access is done.

Signed-off-by: Xiangliang Yu <Xiangliang.Yu@amd.com>
Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>