HWPOISON, hugetlb: enable error handling path for hugepage

This patch just enables handling path. Real containing and
recovering operation will be implemented in following patches.

Dependency:
  "hugetlb, rmap: add reverse mapping for hugepage."

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>