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/net/fec_mxc.c b/drivers/net/fec_mxc.c
index bff5fd1..79f6737 100644
--- a/drivers/net/fec_mxc.c
+++ b/drivers/net/fec_mxc.c
@@ -10,6 +10,7 @@
 
 #include <common.h>
 #include <malloc.h>
+#include <memalign.h>
 #include <net.h>
 #include <netdev.h>
 #include <miiphy.h>