Allow fxp(4) cards with a revision id of 0 to use the 82503 serial
interface as well. This is not an expected revision id per the
datasheet, but unfortunately there are such cards out there with
a 82557 chipset, and they want to use the 82503.

PR: kern/75739
Reported by: Andre Albsmeier <andre.albsmeier@siemens.com>