thermal: core: Introduce thermal_instance_add()

To reduce the number of redundant result checks in
thermal_bind_cdev_to_trip() and make the code in it easier to
follow, move some of it to a new function called thermal_instance_add()
and make thermal_bind_cdev_to_trip() invoke that function.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/3618899.iIbC2pHGDl@rjwysocki.net


Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>