x86: Fix build warning in tables.c when CONFIG_SEABIOS

The following build warning is seen in tables.c:

  warning: implicit declaration of function 'memalign'

Add the missing header file to fix it.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Tested-by: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/x86/lib/tables.c

@@ -5,6 +5,7 @@
  */
 
 #include <common.h>
+#include <malloc.h>
 #include <asm/sfi.h>
 #include <asm/mpspec.h>
 #include <asm/smbios.h>