[SERIAL] Add SupraExpress 56i support

The modem is said to work with belows addition to pnp_dev_table[]:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=296011



Signed-off-by: maximilian attems <janitor@sternwelten.at>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>