kernel - Add safety for Intel SYSRET issue

* First, insofar as we can tell DragonFly was *NOT* vulnerable to the
  Intel SYSRET issue.  We have a RQF_QUICKRET flag that determines if SYSRET
  can be used.  Any heavy weight process switch, signal delivery, signal
  return, or set_regs() call clears this flag and forces the system call to
  return via IRET.

* However, the ptrace() path is a bit convoluted.  Insofar as I can tell
  it just won't allow %rip to be changed unless the target process is in
  a SSTOPped state, meaning that a heavy weight context switch must occur
  before the new %rip is used which means we should be safe.

  Still, we are adding a safety to ptrace_set_pc() to cannonicalize the
  %rip anyway, to ensure that this bug cannot bite us indirectly in the
  future.
drm: Fix locking issues in drm_irq.c

* Some functions expected the drm lock to be used differently than what
  gpu drivers really did, leading to crashes

* Sync them with Linux 3.8.13

Reported-by: Johannes Hofmann
drm/i915: Sync ringbuffer code with Linux 3.8.13

* Split hardware initialization and irq management to model-specific
  functions

* Various little fixes and workarounds to compensate for hardware
  bugs and irregular behavior

* Enable parity error interrupts

* Simplify flushing and request tracking