drm/amdgpu: move reserving GDS/GWS/OA into common code

We don't need that in the per ASIC code.

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