refactor thread struct to keep all changes together

src/threads/thread.h

@@ -104,13 +104,14 @@ struct thread
     struct list_elem donor_elem;        /* List element so that thread can be
                                            enlisted in other donors list. */
 
-    /* Shared between thread.c and synch.c. */
-    struct list_elem elem;              /* List element. */
-
     /* MLFQS items */
     int nice;                           /* Nice value for this thread */
     fp32_t recent_cpu;                  /* Amount of time this process received */
 
+    /* Shared between thread.c and synch.c. */
+    struct list_elem elem;              /* List element. */
+
+
 #ifdef USERPROG
     /* Owned by userprog/process.c. */
     uint32_t *pagedir;                  /* Page directory. */