Fix up some issues with the PX range of cards and add missing IDs.
Fix: PX-257 Revision 3 has 2 ports, not 4.
Added: PX-275/279, PX-475 serial port (LPT is in parport_pc), PX-820 cards
Added/Fix: PX-857 is a variant of PX-803, add note. Add additional card revision
and fix port counts to 2.
Fix: PX-835 is a variant of PX-846, add note
Signed-off-by: Cameron Williams <cang1@xxxxxxxxxx>