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>

net: wwan: t7xx: Add data path interface

Data Path Modem AP Interface (DPMAIF) HIF layer provides methods
for initialization, ISR, control and event handling of TX/RX flows.

DPMAIF TX
Exposes the 'dmpaif_tx_send_skb' function which can be used by the
network device to transmit packets.
The uplink data management uses a Descriptor Ring Buffer (DRB).
First DRB entry is a message type that will be followed by 1 or more
normal DRB entries. Message type DRB will hold the skb information
and each normal DRB entry holds a pointer to the skb payload.

DPMAIF RX
The downlink buffer management uses Buffer Address Table (BAT) and
Packet Information Table (PIT) rings.
The BAT ring holds the address of skb data buffer for the HW to use,
while the PIT contains metadata about a whole network packet including
a reference to the BAT entry holding the data buffer address.
The driver reads the PIT and BAT entries written by the modem, when
reaching a threshold, the driver will reload the PIT and BAT rings.

Signed-off-by: Haijun Liu <haijun.liu@mediatek.com>
Signed-off-by: Chandrashekar Devegowda <chandrashekar.devegowda@intel.com>
Co-developed-by: Ricardo Martinez <ricardo.martinez@linux.intel.com>
Signed-off-by: Ricardo Martinez <ricardo.martinez@linux.intel.com>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>