[SERIAL] serial_cs: convert multi-port table to quirk table

- rename multi_id table to serial_quirk / quirks[]
- use named initialisers
- store a pointer to the quirk table in the serial_info structure
  so we can use the quirk table entry later.
- apply multi-port quirk after the multi-port guessing code,
  but only if it's != -1.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>