serial: clps711x: Add support for N_IRDA line discipline

This patch replace custom handling of IrDA feature with N_IRDA
line discipline, so IrDA mode can be used with irtty driver.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>