ACPI: thermal: Simplify initialization of critical and hot trips

Use the observation that the critical and hot trip points are never
updated by the ACPI thermal driver, because the flags passed from
acpi_thermal_notify() to acpi_thermal_trips_update() do not include
ACPI_TRIPS_CRITICAL or ACPI_TRIPS_HOT, to move the initialization
of those trip points directly into acpi_thermal_get_trip_points() and
reduce the size of __acpi_thermal_trips_update().

Also make the critical and hot trip points initialization code more
straightforward and drop the flags that are not needed any more.

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