net: wwan: t7xx: Add fastboot WWAN port

On early detection of wwan device in fastboot mode, driver sets
up CLDMA0 HW tx/rx queues for raw data transfer and then create
fastboot port to userspace.

Application can use this port to flash firmware and collect
core dump by fastboot protocol commands.
E.g., flash firmware through fastboot port:
 - "download:%08x": write data to memory with the download size.
 - "flash:%s": write the previously downloaded image to the named partition.
 - "reboot": reboot the device.

Link: https://android.googlesource.com/platform/system/core/+/refs/heads/main/fastboot/README.md



Signed-off-by: Jinjian Song <jinjian.song@fibocom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>