bsps/moxie: Use interrupt stack for init stack

Update #3459.

bsps/moxie/moxiesim/start/linkcmds

@@ -267,6 +267,5 @@ SECTIONS
   .debug_funcnames 0 : { *(.debug_funcnames) }
   .debug_typenames 0 : { *(.debug_typenames) }
   .debug_varnames  0 : { *(.debug_varnames) }
-  .stack 0x400000 : { _stack = .; *(.stack) }
   /* These must appear regardless of  .  */
 }

bsps/moxie/moxiesim/start/start.S

@@ -11,7 +11,7 @@
         .text
         .global _start
 _start:
-        ldi.l   $sp, _stack     /* load up stack pointer */
+        ldi.l   $sp, _ISR_Stack_area_end /* load up stack pointer */
         xor     $fp, $fp        /* zero fp to allow unwinders to stop */
 
         /* zero the bss area */