ACPI: thermal: Drop critical_valid and hot_valid trip flags

The critical_valid and hot_valid flags in struct acpi_thermal_trips are
only used during initialization and they are only false if the
corresponding trip temperatures are equal to THERMAL_TEMP_INVALID, so
drop them and use THERMAL_TEMP_INVALID checks instead of them where
applicable.

No intentional functional impact.

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