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/drivers/usb/gadget/ether.c b/drivers/usb/gadget/ether.c
index 53f4672..c5e35ee 100644
--- a/drivers/usb/gadget/ether.c
+++ b/drivers/usb/gadget/ether.c
@@ -17,6 +17,7 @@
 #include <net.h>
 #include <usb.h>
 #include <malloc.h>
+#include <memalign.h>
 #include <linux/ctype.h>
 
 #include "gadget_chips.h"