Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

drm/i915: Add HW context support

This feature is required by Mesa 9.2+. Without this, a GL application
crashes with the following message:
# glxinfo
name of display: :0.0
Gen6+ requires Kernel 3.6 or later.
Assertion failed: (ctx->Version > 0), function handle_first_current,
file ../../src/mesa/main/context.c, line 1498.
Abort (core dumped)

Now, Mesa 10.2.4 and 10.3-rc3 works fine:
# glxinfo
name of display: :0
display: :0 screen: 0
direct rendering: Yes
...
OpenGL renderer string: Mesa DRI Intel(R) 965GM
OpenGL version string: 2.1 Mesa 10.2.4
...

The code was imported from Linux 3.8.13.

This an MFC of r271705.

Approved by: re (glebius)
Reviewed by: kib@
Tested by: kwm@, danfe@, Henry Hu,
Lundberg, Johannes <johannes@brilliantservice.co.jp>,
Johannes Dieterich <dieterich.joh@gmail.com>,
Lutz Bichler <lutz.bichler@gmail.com>,
Relnotes: yes

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Add the code for new Intel GPU driver, which supports GEM, KMS and
works with new generations of GPUs (IronLake, SandyBridge and
supposedly IvyBridge).

The driver is not connected to the build yet.

Sponsored by: The FreeBSD Foundation
MFC after: 1 week