ACPI / watchdog: Prefer iTCO_wdt on Lenovo Z50-70

WDAT table on Lenovo Z50-70 is using RTC SRAM (ports 0x70 and 0x71) to
store state of the timer. This conflicts with Linux RTC driver
(rtc-cmos.c) who fails to reserve those ports for itself preventing RTC
from functioning. In addition the WDAT table seems not to be fully
functional because it does not reset the system when the watchdog times
out.

On this system iTCO_wdt works just fine so we simply prefer to use it
instead of WDAT. This makes RTC working again and also results working
watchdog via iTCO_wdt.

Reported-by: Peter Milley <pbmilley@gmail.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=199033


Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>