Fix lcd not waking up when backlight is always off

This patch is relevant for targets with a transflective display.
If the backlight was set to "always off" (e.g. to use the lcd
in a pure passive way), and the sleep timer ran off, the LCD
would stay disabled and didn't wake up when a button is pressed.

Change-Id: I0a157c7f421d9fc4c7d8ba903f2cf93f6cef51d0

firmware/backlight.c

@@ -499,6 +499,10 @@ static void backlight_update_state(void)
     if (UNLIKELY(timeout < 0))
     {
         do_backlight_off();
+#if defined(HAVE_TRANSFLECTIVE_LCD) && defined(HAVE_LCD_SLEEP)
+        /* LCD must be enabled to allow "passive" operation (backlight always off) */
+        lcd_awake();
+#endif
 #if (CONFIG_BACKLIGHT_FADING == BACKLIGHT_FADING_SW_SETTING) \
     || (CONFIG_BACKLIGHT_FADING == BACKLIGHT_FADING_SW_HW_REG)
         /* necessary step to issue fading down when the setting is selected */

firmware/export/backlight.h

@@ -64,6 +64,10 @@ void lcd_set_sleep_after_backlight_off(int timeout_seconds);
 void lcd_awake(void);
 #endif
 
+#ifdef HAVE_LCD_SLEEP
+void lcd_awake(void);
+#endif
+
 #else /* !HAVE_BACKLIGHT */
 #define backlight_init()
 #endif /* !HAVE_BACKLIGHT */