watchdog: it87_wdt: Add support for IT8720F watchdog

This simple patch adds support for a watchdog in IT8720F Super IO chip
to it87_wdt driver.

Signed-off-by: Ondrej Zajicek <santiago@crfreenet.org>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>