Support Write-Through mapping on x86

This patchset adds support of Write-Through (WT) mapping on x86.
The study below shows that using WT mapping may be useful for
non-volatile memory.

  http://www.hpl.hp.com/techreports/2012/HPL-2012-236.pdf

All new/modified interfaces have been tested.

v7:
 - Rebased to 3.19-rc3 as Juergen's patchset for the PAT management
   has been accepted.

v6:
 - Dropped the patch moving [set|get]_page_memtype() to pat.c
   since the tip branch already has this change.
 - Fixed an issue when CONFIG_X86_PAT is not defined.

v5:
 - Clarified comment of why using slot 7. (Andy Lutomirski,
   Thomas Gleixner)
 - Moved [set|get]_page_memtype() to pat.c. (Thomas Gleixner)
 - Removed BUG() from set_page_memtype(). (Thomas Gleixner)

v4:
 - Added set_memory_wt() by adding WT support of regular memory.

v3:
 - Dropped the set_memory_wt() patch. (Andy Lutomirski)
 - Refactored the !pat_enabled handling. (H. Peter Anvin,
   Andy Lutomirski)
 - Added the picture of PTE encoding. (Konrad Rzeszutek Wilk)

v2:
 - Changed WT to use slot 7 of the PAT MSR. (H. Peter Anvin,
   Andy Lutomirski)
 - Changed to have conservative checks to exclude all Pentium 2, 3,
   M, and 4 families. (Ingo Molnar, Henrique de Moraes Holschuh,
   Andy Lutomirski)
 - Updated documentation to cover WT interfaces and usages.
   (Andy Lutomirski, Yigal Korman)

---
Toshi Kani (7):
  1/7 x86, mm, pat: Set WT to PA7 slot of PAT MSR
  2/7 x86, mm, pat: Change reserve_memtype() to handle WT
  3/7 x86, mm, asm-gen: Add ioremap_wt() for WT
  4/7 x86, mm, pat: Add pgprot_writethrough() for WT
  5/7 x86, mm, pat: Refactor !pat_enable handling
  6/7 x86, mm, asm: Add WT support to set_page_memtype()
  7/7 x86, mm: Add set_memory_wt() for WT

---
 Documentation/x86/pat.txt            |  13 ++-
 arch/x86/include/asm/cacheflush.h    |   6 +-
 arch/x86/include/asm/io.h            |   2 +
 arch/x86/include/asm/pgtable_types.h |   3 +
 arch/x86/mm/init.c                   |   6 +-
 arch/x86/mm/iomap_32.c               |  12 +--
 arch/x86/mm/ioremap.c                |  26 ++++-
 arch/x86/mm/pageattr.c               |  61 ++++++++++--
 arch/x86/mm/pat.c                    | 184 ++++++++++++++++++++++++-----------
 include/asm-generic/io.h             |   9 ++
 include/asm-generic/iomap.h          |   4 +
 include/asm-generic/pgtable.h        |   4 +
 12 files changed, 244 insertions(+), 86 deletions(-)

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