aboot: move mmu disable to conditional compilation

Change-Id: I9f655cef762e14570a127ef5bea1a32aa08af32d
diff --git a/app/aboot/aboot.c b/app/aboot/aboot.c
index dbcd8dd..9b5151c 100644
--- a/app/aboot/aboot.c
+++ b/app/aboot/aboot.c
@@ -418,7 +418,9 @@
 	 * Will need to revisit to find the root cause.
 	 */
 	dsb();
+#if ARM_WITH_MMU
 	arch_disable_mmu();
+#endif
 	entry(0, machtype, tags);
 }