core: dprintf on malloc/free if -DDEBUG_MALLOC

When dynamic debug is engaged, the output is pretty flooded by
malloc/free messages while you are looking at other traces.

As devel.mk have a DEBUG_MALLOC option, it seems pretty logical to
enable the malloc/free dprintf() only if this option is engaged.

That patch make the dynamic debug output less floody while letting the
choice to get the malloc/free dprintf() messages.

core/mem/free.c

@@ -87,7 +87,9 @@ void bios_free(void *ptr)
 
 __export void free(void *ptr)
 {
+#ifdef DEBUG_MALLOC
     dprintf("free(%p) @ %p\n", ptr, __builtin_return_address(0));
+#endif
 
     if ( !ptr )
         return;

core/mem/malloc.c

@@ -93,14 +93,18 @@ static void *_malloc(size_t size, enum heap heap, malloc_tag_t tag)
 {
     void *p;
 
+#ifdef DEBUG_MALLOC
     dprintf("_malloc(%zu, %u, %u) @ %p = ",
 	size, heap, tag, __builtin_return_address(0));
+#endif
 
     sem_down(&__malloc_semaphore, 0);
     p = firmware->mem->malloc(size, heap, tag);
     sem_up(&__malloc_semaphore);
 
+#ifdef DEBUG_MALLOC
     dprintf("%p\n", p);
+#endif
     return p;
 }