Export asus_wmi_evaluate_method() and related headers for use by other
drivers.

hid-asus is going to use this to avoid advertising that it has a keyboard
backlight when the keyboard backlight is controlled via WMI.
Signed-off-by: Daniel Drake <drake@endlessm.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>