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_common.c b/fs/ext4/ext4_common.c
index cab5465..c77e22d 100644
--- a/fs/ext4/ext4_common.c
+++ b/fs/ext4/ext4_common.c
@@ -24,6 +24,7 @@
 #include <ext4fs.h>
 #include <inttypes.h>
 #include <malloc.h>
+#include <memalign.h>
 #include <stddef.h>
 #include <linux/stat.h>
 #include <linux/time.h>