drm/amdgpu: Move memory partition query to gmc

GMC block handles memory related information, it makes more sense to
keep memory partition functions in gmc block.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Le Ma <le.ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>