Make LCD_TIMEOUT_TO_STATUS configurable

As suggested in
https://github.com/MarlinFirmware/Marlin/issues/5570#issuecomment-283059
065

Marlin/Conditionals_post.h

@@ -726,4 +726,9 @@
     #define HAS_FOLDER_SORTING (FOLDER_SORTING || ENABLED(SDSORT_GCODE))
   #endif
 
+  // LCD timeout to status screen default is 15s
+  #ifndef LCD_TIMEOUT_TO_STATUS
+    #define LCD_TIMEOUT_TO_STATUS 15000
+  #endif
+
 #endif // CONDITIONALS_POST_H