net: wwan: t7xx: Add NAPI support

Replace the work queue based RX flow with a NAPI implementation
Remove rx_thread and dpmaif_rxq_work.
Enable GRO on RX path.
Introduce dummy network device. its responsibility is
    - Binds one NAPI object for each DL HW queue and acts as
      the agent of all those network devices.
    - Use NAPI object to poll DL packets.
    - Helps to dispatch each packet to the network interface.

Signed-off-by: Haijun Liu <haijun.liu@mediatek.com>
Co-developed-by: Sreehari Kancharla <sreehari.kancharla@linux.intel.com>
Signed-off-by: Sreehari Kancharla <sreehari.kancharla@linux.intel.com>
Signed-off-by: Chandrashekar Devegowda <chandrashekar.devegowda@intel.com>
Acked-by: Ricardo Martinez <ricardo.martinez@linux.intel.com>
Acked-by: M Chetan Kumar <m.chetan.kumar@linux.intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>