drm: Import linux/workqueue.h from FreeBSD's OFED stack
linux/timer.h: Add round_jiffies_up_relative()
linux/workqueue.h: Adapt to DragonFly

* Protect callout structures from concurrent operations on MP machines

* Add some functions used by the drm/i915 code from Linux 3.8.x
drm/i915: Use the Linux workqueue API

Opportunistically reduce differences with Linux 3.8.13