drm/amdgpu: Fix GRBM programming sequence

It needs to be done only for XCC instances in non-AID0. Use the physical
instance to determine non-AID0 XCC instances.

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>