drivers: watchdog: Add Intel TCO Watchdog driver

This adds a basic Intel TCO watchdog driver. The driver doesn't support
windowed timeouts (a non-zero window.min value) or callbacks. The driver
currently assumes TCO version 6, which can be found e.g. on Elkhart Lake
and Raptor Lake platforms. The driver also expects the TCOBA base
address to be specified through DTS, rather than doing runtime lookup
(using e.g. ACPI or PCIe).

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>