drm/amdgpu: move amdgpu_device_(vram|gtt)_location

Move that into amdgpu_gmc.c since we are really deadling with GMC
address space here.

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