Move ALLOC_CACHE_ALIGN_BUFFER() to the new memalign.h header

Now that we have a new header file for cache-aligned allocation, we should
move the stack-based allocation macro there also.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/fs/ext4/ext4_write.c b/fs/ext4/ext4_write.c
index fbc4c4b..d346c06 100644
--- a/fs/ext4/ext4_write.c
+++ b/fs/ext4/ext4_write.c
@@ -23,6 +23,7 @@
 
 
 #include <common.h>
+#include <memalign.h>
 #include <linux/stat.h>
 #include <div64.h>
 #include "ext4_common.h"