drm/amdgpu: enable cp_fw_write_wait for navy_flounder

It's the same with sienna_cichlid, cp fw for navy_flounder
can support WAIT_REG_MEM packet.

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>