watchdog: sp5100_tco: Add support for recent FCH versions

Starting with Family 16h Models 30h-3Fh and Family 15h Models 60h-6Fh,
watchdog address space decoding has changed. The cutover point is already
identified in the i2c-piix2 driver, so use the same mechanism.

Cc: Zoltán Böszörményi <zboszor@pr.hu>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>