thermal: netlink: Add the commands and the events for the thresholds

The thresholds exist but there is no notification neither action code
related to them yet.

These changes implement the netlink for the notifications when the
thresholds are crossed, added, deleted or flushed as well as the
commands which allows to get the list of the thresholds, flush them,
add and delete.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://patch.msgid.link/20241022155147.463475-3-daniel.lezcano@linaro.org


[ rjw: Use the thermal_zone guard for locking, subject edit ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>