drm2: Synchronize with FreeBSD

as of r253709 (2013-07-27): The pmap_qenter() and pmap_qremove() perform
TLB invalidation on its own, no need to call pmap_invalidate_range() one
more time.
acpi/pstate: AMD CPUs' Family >= 10h use same P-State controls

While I'm here, clean up the code little bit by using CPUID_TO_FAMILY
and cpu_exthigh.
drm/i915: Do not check only primary displays

* On IBM-PC compatible systems, only one graphic adapter can be
  VGA-compatible at the same time

* This adapter is marked with the PCIS_DISPLAY_VGA capability in
  the PCI device list

* With KMS, we do not care about VGA compatibility anymore; let's
  just use whatever hardware is present

* Tested-with: A radeon X550 as primary display adapter
kernel/drm2: Remove two unused externs.