drm/amdgpu: configure navy_flounder gfx according to gfx 10.3

The gfx version of navy_flounder is 10.3, identical to
sienna_cichlid, follow the way of sienna_cichlid.

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