watchdog: f71808e_wdt: Add F81866 support

Adds watchdog enable support for Fintek F81866 Super-IO chip to
Fintek wdt driver (f71808e_wdt)

Tested and verified on iBASE MI802 Industrial PC

Datasheet references:
http://www.alldatasheet.com/datasheet-pdf/pdf/459085/FINTEK/F81866AD-I.html



Suggested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Ji-Ze Hong (Peter Hong) <hpeter+linux_kernel@gmail.com>
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>