[WATCHDOG] wdt_pci.c: remove #ifdef CONFIG_WDT_501_PCI

Change the wdt_pci.c watchdog driver so that the code is the same for
both the PCI-WDT500 as the PCI-WDT501 card. The selection of the card
is now being done via the module parameter: 'type' instead of the
config option CONFIG_WDT_501_PCI.

Signed-off-by: Wim Van Sebroeck <wim@iguana.be>