Report the size of pages backing VMAs in /proc V3

The following two patches add support for printing the size of pages used by
the kernel and the MMU to back VMAs. This can be used by a user to verify
that a hugepage-aware application is using the expected page sizes.

The first patch prints the size of page used by the kernel when allocating
pages for a VMA in /proc/pid/smaps. The second patch reports on
the size of page used by the MMU as it can differ - for example on POWER
using 64K as a base pagesize on older processors.

Changelog since V2
  o Drop changes to /proc/pid/maps - could not get agreement and it affects
    procps. Patch to procps was posted but fell into silence. Dropping
    patch as smaps gives the necessary information, just with a bit more
    legwork by the user
  o Drop redundant VM_BUG_ON (Alexey)

Changelog since V1
  o Fix build failure on !CONFIG_HUGETLB_PAGE
  o Uninline helper functions
  o Distinguish between base pagesize and MMU pagesize

 arch/powerpc/include/asm/hugetlb.h |    6 ++++++
 arch/powerpc/mm/hugetlbpage.c      |    7 +++++++
 fs/proc/task_mmu.c                 |    8 ++++++--
 include/linux/hugetlb.h            |    6 ++++++
 mm/hugetlb.c                       |   29 +++++++++++++++++++++++++++++
 5 files changed, 54 insertions(+), 2 deletions(-)