Align global_data to a 16-byte boundary

Some archs like to have larger alignment for their global data. Use 16 bytes
which suits all current archs.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

include/asm-generic/global_data.h

@@ -99,7 +99,8 @@ typedef struct global_data {
 	int pcidelay_done;
 #endif
 	struct udevice *cur_serial_dev;	/* current serial device */
-	struct arch_global_data arch;	/* architecture-specific data */
+	/* arch-specific data */
+	struct arch_global_data arch __attribute__((aligned(16)));
 } gd_t;
 #endif