thermal: trip: Add conversion macros for thermal trip priv field

Some drivers will need to store integers in the priv field of struct
thermal_trip, so add conversion macros for doing this in a consistent
way and switch over the int340x_thermal driver that already does it and
uses custom conversion functions to using the new macros.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/3297884.aeNJFYEL58@rjwysocki.net