watchdog: new driver for VIA chipsets

New driver for the hardware watchdog timer on VIA chipsets.
This driver uses the new watchdog framework.
PnP must be enabled in BIOS to get full control of watchdog registers.
The timer code has been added by Wim Van Sebroeck.
Tested on a Artigo A1100, VX855 chipset.

Signed-off-by: Marc Vertes <marc.vertes@sigfox.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>