ACPI: thermal: Drop struct acpi_thermal_flags

Drop struct acpi_thermal_flags which is not really used (only one
flag in it is ever set, but it is never read) and call
acpi_execute_simple_method() directly to evaluate _SCP instead of
using acpi_thermal_set_cooling_mode(), which has no callers after
that change, so drop it.

No intentional functional impact.

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