thermal: core: Separate thermal zone governor initialization

thermal: core: Separate thermal zone governor initialization

In preparation for a subsequent change that will switch over the thermal
core to using a mutex guard for managing thermal_governor_lock, move
the code running in thermal_zone_device_register_with_trips() under that
lock into a separate function called thermal_zone_init_governor().

While at it, drop a useless comment.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/4408795.ejJDZkT8p0@rjwysocki.net
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>