BugLink: https://launchpad.net/bugs/1645591

Import USB UART driver from
https://www.exar.com/design-tools/software-drivers

Product Family: USB UART
Part Numbers:
	XR21V1410, XR21V1412, XR21V1414,
	XR21B1411, XR21B1420, XR21B1422,
	XR21B1424, XR22801, XR22802,
	XR22804
Operating system: Linux 3.6.x and newer
Driver version: 1A
Release date: January 2015
Signed-off-by: Wen-chien Jesse Sung <jesse.sung@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>