Add property to set exclusivity

Disabling the serial port driver's exclusive mode is necessary for
pseudo serial ports and some USB/serial adapters to work correctly.

Change-Id: I74d45feed619817b61e265b00aec8b0ebfae7a33
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>
Reviewed-by: Denis Shienkov <denis.shienkov@gmail.com>