serial: RS485 termination is supported if DT provides one

When DT provides rs485-term, set termination flag as supported.

Reviewed-by: Lino Sanfilippo <l.sanfilippo@kunbus.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220704094515.6831-3-ilpo.jarvinen@linux.intel.com


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