watchdog: iTCO: Add support for Cannon Lake PCH iTCO

In Intel Cannon Lake PCH the NO_REBOOT bit was moved from the private
register space to be part of the TCO1_CNT register. For this reason
introduce another version (6) that uses this register to set and clear
NO_REBOOT bit.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>