usb-serial: implement break event.

usb-serial: implement break event.

Implement the serial break via usb serial.

The second data byte in ftdi status packet contains the break status.
The values were already defined in usb-serial.c so it was a matter of
making use of the event_trigger to form a urb to send over to the host
controller with the serial break status set.

This was tested against a linux development image which enables sysrq
via a serial break on the ftdi usb console.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>