apple-gmux: Add suspend/resume support for the backlight

After S3, the brightness might not be restored to the pre-suspend value.
Request status update calls from the backlight core on suspend/resume to
ensure the brightness value is restored.

Reported-and-tested-by: Austin Lund <austin.lund@gmail.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>

drivers/platform/x86/apple-gmux.c

@@ -87,6 +87,9 @@ static int gmux_update_status(struct backlight_device *bd)
 	struct apple_gmux_data *gmux_data = bl_get_data(bd);
 	u32 brightness = bd->props.brightness;
 
+	if (bd->props.state & BL_CORE_SUSPENDED)
+		brightness = 0;
+
 	/*
 	 * Older gmux versions require writing out lower bytes first then
 	 * setting the upper byte to 0 to flush the values. Newer versions
@@ -102,6 +105,7 @@ static int gmux_update_status(struct backlight_device *bd)
 }
 
 static const struct backlight_ops gmux_bl_ops = {
+	.options = BL_CORE_SUSPENDRESUME,
 	.get_brightness = gmux_get_brightness,
 	.update_status = gmux_update_status,
 };