thermal: core: Use kstrdup_const() during cooling device registration

Some *thermal_cooling_device_register() calls pass a string literal as
the 'type' parameter, so kstrdup_const() can be used instead of
kstrdup() to avoid a memory allocation in such cases.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>