[WATCHDOG] Add driver for winbond w83697ug/uf watchdog feature

Adapted the w83627hf_wdt.c driver to work with the w83697ug/uf chip, 
found on MSI Fuzzy CX700 boards.

The method used is taken directly from the winbond datasheet and 
surprisingly it differs slightly from all the other winbond watchdogs.

So far it has only been tested on the CX700 board that I have, but it 
seems to work nicely.

Signed-off-by: Flemming Frandsen <ff@nrvissing.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>