ACPI: thermal: Simplify critical and hot trips representation

Notice that the only piece of information regarding the critical and hot
trips that needs to be stored in the driver's local data structures is
whether or not these trips are valid, so drop all of the redundant
information from there and adjust the code accordingly.

Among other things, this requires acpi_thermal_add() to be rearranged
so as to obtain the critical trip temperature before populating the trip
points table and for symmetry, the hot trip temperature is obtained
earlier too.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>