Replace non critical PANIC with DEBUGPANIC to save the code space

arch/xtensa/src/common/xtensa_exit.c

@@ -202,5 +202,5 @@ void _exit(int status)
    * interrupts are disabled.
    */
 
-  PANIC();
+  DEBUGPANIC();
 }

arch/xtensa/src/common/xtensa_reprioritizertr.c

@@ -90,7 +90,7 @@ void up_reprioritize_rtr(struct tcb_s *tcb, uint8_t priority)
 #endif
     )
     {
-       PANIC();
+       DEBUGPANIC();
     }
   else
     {