[Intel-gfx] add remap_pfn_range_notrack instead of reinventing it in i915 v2

[Christoph Hellwig]

Hi all,

i915 has some reason to want to avoid the track_pfn_remap overhead in
remap_pfn_range.  Add a function to the core VM to do just that rather
than reinventing the functionality poorly in the driver.

Note that the remap_io_sg path does get exercises when using Xorg on my
Thinkpad X1, so this should be considered lightly tested, I've not
managed to hit the remap_io_mapping path at all.

Changes since v1:
 - create a io_mapping_map_user wrapper instead of exporting
   remap_pfn_range_notrack
 - switch to plain remap_pfn_range for remap_sg as it does not use
   a pre-verified pgprot from an iomap

Diffstat:
 drivers/gpu/drm/i915/Kconfig             |    1 
 drivers/gpu/drm/i915/gem/i915_gem_mman.c |    9 +-
 drivers/gpu/drm/i915/i915_drv.h          |    3 
 drivers/gpu/drm/i915/i915_mm.c           |  117 ++++++-------------------------
 include/linux/io-mapping.h               |    3 
 include/linux/mm.h                       |    2 
 mm/Kconfig                               |    3 
 mm/Makefile                              |    1 
 mm/io-mapping.c                          |   29 +++++++
 mm/memory.c                              |   51 ++++++++-----
 10 files changed, 97 insertions(+), 122 deletions(-)