asus-wmi: control backlight power through WMI, not ACPI

BugLink: https://bugs.launchpad.net/bugs/1000146

Some h/w that can adjust screen brightness through ACPI functions, but
can't turn on/off the backlight power correctly. So, we list those h/w in
quirks and try to turn on/off the backlight power through WMI.
Signed-off-by: AceLan Kao <acelan.kao@canonical.com>
Signed-off-by: Corentin Chary <corentin.chary@gmail.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>
diff --git a/drivers/platform/x86/asus-wmi.h b/drivers/platform/x86/asus-wmi.h
index d43b667..9c1da8b 100644
--- a/drivers/platform/x86/asus-wmi.h
+++ b/drivers/platform/x86/asus-wmi.h
@@ -39,6 +39,7 @@
 	bool hotplug_wireless;
 	bool scalar_panel_brightness;
 	bool store_backlight_power;
+	bool wmi_backlight_power;
 	int wapf;
 };