recovery: Porting screensave mode for new platform.

On new board platform the brightness path of
sys/class/leds/lcd-backlight is deprecated,instead of
/sys/class/backlight/panel0-backlight/.

Test: reboot into recovery on sdm845.
Change-Id: Idf0027ab888f9f982a8eef7de230ce3635e7c300
Signed-off-by: katao <katao@xiaomi.com>
diff --git a/ui.h b/ui.h
index 4086023..4c54d69 100644
--- a/ui.h
+++ b/ui.h
@@ -148,6 +148,8 @@
   // be configured via subclassing. Setting brightness_normal_ to 0 to disable screensaver.
   unsigned int brightness_normal_;
   unsigned int brightness_dimmed_;
+  std::string brightness_file_;
+  std::string max_brightness_file_;
 
   // Whether we should listen for touch inputs (default: false).
   bool touch_screen_allowed_;