drm/amdgpu: add get_retire_flip_bits for UMC

Add the general interface to get flip bits for RAS bad page retirement.

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>