thermal: gov_power_allocator: Set up trip points earlier

Set up the trip points at the beginning of the binding function.

This simplifies the code a bit and allows for further cleanups.

Also add a check to fail the binding if the last passive trip point is
not found.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
[ rjw: Changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>