thermal: gov_power_allocator: Use .manage() callback instead of .throttle()

The Power Allocator governor really only wants to be called once per
thermal zone update and it does a special check to skip the extra,
from its perspective, invocations of the .throttle() callback.

Make it use .manage() instead of .throttle().

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>