serial_cs: Add Option International GSM-Ready 56K/ISDN modem

Add support for Option International GSM-Ready 56K/ISDN PCMCIA modem
card.

Signed-off-by: Ondrej Zary <linux@zary.sk>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210611201940.23898-2-linux@zary.sk


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