drm/i915: Update to Linux 3.14

drm/i915: Update to Linux 3.14

Changes specific to the DragonFly driver:

* Most GEM code paths are now similar to Linux, leading to increased
  stability and performance.
  Making this change was greatly helped by studying the OpenBSD code.

* We were previously using legacy functions to set up page table entries and
  this was starting to become a serious problem on particular platforms such
  as gen4 or Broadwell. As of this commit, we now use the same chip-specific
  virtual functions as Linux.

* RC6 and Frame Buffer Compression power savings enabled by default, depending
  on the GPU family

Changes brought by the Linux 3.11 => 3.14 driver update:

* Various bug fixes on all GPU generations, especially stability improvements

* Power consumption improvements

* Many Valleyview/Baytrail support improvements

* The giant 128MB L4 cache is now enabled when present on Haswell

* Added support for Broadwell GPUs

* HDMI 4K support

* basic support for 3D/stereo displays on HDMI