USB: serial: add Moxa UPORT 11x0 driver

Add a driver which supports :

- UPort 1110  : 1 port RS-232 USB to Serial Hub.
- UPort 1130  : 1 port RS-422/485 USB to Serial Hub.
- UPort 1130I : 1 port RS-422/485 USB to Serial Hub with Isolation.
- UPort 1150  : 1 port RS-232/422/485 USB to Serial Hub.
- UPort 1150I : 1 port RS-232/422/485 USB to Serial Hub with Isolation.

This driver is based on GPL MOXA driver written by Hen Huang and available
on MOXA website. The original driver was based on io_ti serial driver.

Signed-off-by: Mathieu OTHACEHE <m.othacehe@gmail.com>
Signed-off-by: Johan Hovold <johan@kernel.org>