mm/memory-failure.c: add page flag description in error paths

It helps to provide page flag description along with the raw value in
error paths during soft offline process.  From sample experiments

Before the patch:

  soft offline: 0x6100: migration failed 1, type 3ffff800008018
  soft offline: 0x7400: migration failed 1, type 3ffff800008018

After the patch:

  soft offline: 0x5900: migration failed 1, type 3ffff800008018 (uptodate|dirty|head)
  soft offline: 0x6c00: migration failed 1, type 3ffff800008018 (uptodate|dirty|head)

Link: http://lkml.kernel.org/r/20170409023829.10788-1-khandual@linux.vnet.ibm.com
Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>