x86: customize the malloced address to be 16-byte aligned

That can gain better memory performance than 8-byte alignment

Change-Id: Ibcc5bf7b96ed10166038357dd0c86c9171768f3e
Signed-off-by: Jack Ren <jack.ren@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>