Consolidate arch-specific mem_malloc_init() implementations

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
diff --git a/include/malloc.h b/include/malloc.h
index 0382169..3e145ad 100644
--- a/include/malloc.h
+++ b/include/malloc.h
@@ -944,6 +944,8 @@
 extern ulong mem_malloc_end;
 extern ulong mem_malloc_brk;
 
+void mem_malloc_init(ulong start, ulong size);
+
 #ifdef __cplusplus
 };  /* end of extern "C" */
 #endif