This adds support for watchdog part of Fintek F71868 Super I/O chip to
f71808e_wdt driver.

The F71868 chip is, in general, very similar to a F71869, however it has
slightly different set of available reset pulse widths.

Tested on MSI A55M-P33 motherboard.
Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>