ACPI: thermal: Eliminate struct acpi_thermal_state_flags

Notice that the enabled flag is only needed for active trip points,
so drop struct acpi_thermal_state_flags, add a simple "bool valid" field
to the definitions of all trip point structures instead of flags and
add a "bool enabled" field to struct acpi_thermal_active.

Adjust the code using the modified structures accordingly.

No intentional functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Michal Wilczynski <michal.wilczynski@intel.com>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>