fl16: On sleep pin only turn off backlight

Other low power states should be handled perfectly fine by USB suspend,
since this is now fixed in chibios.

Signed-off-by: Daniel Schaefer <dhs@frame.work>

quantum/backlight/backlight.c

@@ -104,6 +104,14 @@ void backlight_enable(void) {
     backlight_set(backlight_config.level);
 }
 
+void backlight_enable_old_level(void) {
+    if (backlight_config.enable) return; // do nothing if backlight is already on
+
+    eeconfig_update_backlight(backlight_config.raw);
+    dprintf("backlight enable\n");
+    backlight_set(backlight_config.level);
+}
+
 /** \brief Disable backlight
  *
  * FIXME: needs doc

quantum/backlight/backlight.h

@@ -49,6 +49,7 @@ _Static_assert(sizeof(backlight_config_t) == sizeof(uint8_t), "Backlight EECONFI
 void    backlight_init(void);
 void    backlight_toggle(void);
 void    backlight_enable(void);
+void    backlight_enable_old_level(void);
 void    backlight_disable(void);
 bool    is_backlight_enabled(void);
 void    backlight_step(void);