thermal: core: Update thermal zone registration documentation

The thermal sysfs API document is outdated.  One of the problems with
it is that is still documents thermal_zone_device_register() which
does not exit any more and it does not reflect the current thermal
zone operations definition.

Replace the thermal_zone_device_register() description in it with
a thermal_zone_device_register_with_trips() description, including
an update of the thermal zone operations list.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://patch.msgid.link/2767845.mvXUDI8C0e@rjwysocki.net