drm/amdgpu: add gfx ip block for navy_flounder

since navy_flounder has similar gc IP version with
sienna_cichlid, follow its setting for the moment.

Signed-off-by: Jiansong Chen <Jiansong.Chen@amd.com>
Reviewed-by: Tao Zhou <Tao.Zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>