drm/i915: Update to Linux 3.16

drm/i915: Update to Linux 3.16

* Much improved support for Broadwell GPUs. Acceleration should now be fully
  operational and the giant L4 eDRAM cache is now enabled when present.

* Baytrail/Valleyview support improvements

* prelimary support for Cherryview (14nm Atom SOCs)

* Various fixes and performance improvements on most other GPU generations

* Improved runtime power management

* 5.4GHz DisplayPort support

* Large cursor support (up to 256x256 pixels), useful for high-dpi displays.

* Mapping of user pages into video memory (userptr)
  This allows zero-copy downloads and efficient readback to/from the GPU,
  allowing faster rendering of client-side software rasterisers, mitigation
  of stalls due to read back and faster pipelining of texture data (such as
  pixel buffer objects in GL or data blobs in CL). Mixed CPU/GPU operations
  become more efficient in general.