Fix arm926ejs compile when SKIP_LOWLEVEL_INIT is on

Fix arm926ejs compile when SKIP_LOWLEVEL_INIT is on.

cpu/arm926ejs/start.o: In function `cpu_init_crit':
.../cpu/arm926ejs/start.S:227: undefined reference to `lowlevel_init'
Signed-off-by: NStelian Pop <stelian@popies.net>

cpu/arm926ejs/start.S

@@ -198,8 +198,7 @@ _start_armboot:
  *
  *************************************************************************
  */
-
-
+#ifndef CONFIG_SKIP_LOWLEVEL_INIT
 cpu_init_crit:
 	/*
 	 * flush v4 I/D caches
@@ -225,6 +224,8 @@ cpu_init_crit:
 	bl	lowlevel_init	/* go setup pll,mux,memory */
 	mov	lr, ip		/* restore link */
 	mov	pc, lr		/* back to my caller */
+#endif /* CONFIG_SKIP_LOWLEVEL_INIT */
+
 /*
  *************************************************************************
  *