serial: 8250_lpss: Enable PSE UART Auto Flow Control

Add a call to the custom ->set_termios() which has implementation about
changing the state of RTS and CTS.

Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Aman Kumar <aman.kumar@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20211005133026.21488-2-andriy.shevchenko@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>