watchdog: Use module_pci_driver

This patch converts the PCI watchdog drivers so that they use the
module_pci_driver() macro. This makes the code smaller and simpler.

Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Cc: Thomas Mingarelli <thomas.mingarelli@hp.com>
Cc: Marc Vertes <marc.vertes@sigfox.com>