Intel GPU driver import

With r235375, all required VM support for new Intel GPU driver was
committed into HEAD. There are still some things to improve and
change, but now the all.14.9.patch does not touch anything outside agp
or drm.  This allows to start the process of importing the new Intel
GPU driver into HEAD.

I am writing this as initial head-up and to discuss some questions,
for which I do have answers but would prefer to have additional
feedback from people doing Xorg work.

The patch as-is just replaces the Intel DRI1 bits with DRI2
driver. Patch added most of the KMS infrastructure into DRM
core. Also, patch completely changed the locking model used by Intel
driver. I made absolutely minimal efforts needed to keep other DRI1
drivers compilable. Despite that, I got several surpising reports that
Radeon DRI1 still works.

That said, for import I can (first choice) just apply the patch,
replacing the Intel driver with new one. Or (second choice) I may
create another directory, say sys/dev/drm2, and import _only_ Intel
driver together with updated DRM core, there.

The positive points to the second approach is that we still have older
kernel drivers around. Also, I have more freedom in changing the DRM
core, without fearing breakage in the DRI1 land. Since I do not really
want to deal with Gen2-3 hardware, and VGA console does not work with
new driver (yet), there are definite advantages.

On the other hand, driver automatic loading will not work with
dev/drm2 approach. New driver have to use different module name to
co-exist with dri1 driver, so ddx driver cannot load new driver by old
name. As result, users need to manually kldload new driver before
starting Xorg.

My own preference is to implement second choice and put the driver
into dev/drm2.