drm/radeon: Import the Radeon KMS driver

This driver is based on Linux 3.8 and a previous effort by kan@.

More informations about this project can be found on the FreeBSD wiki:
    https://wiki.freebsd.org/AMD_GPU

The driver is split into:

  sys/dev/drm2:
    The driver sources.

  sys/modules/drm2/radeonkmw:
    The driver main kernel module's Makefile.

  sys/modules/drm2/radeonkmsfw:
    All firmware kernel module Makefiles. There's one directory and one
    Makefile for each firmware.

  sys/contrib/dev/drm2/radeonkmsfw:
    All firmware binary sources.

  tools/tools/drm/radeon
    Tools to update firmwares or regenerate some headers.

Merging the driver to FreeBSD 9.x may be possible but not a priority for
now.

Help from:	kib@, kan@
Tested by:	avg@, kwm@, ray@,
		Alexander Yerenkow <yerenkow@gmail.com>,
		Anders Bolt-Evensen <andersbo87@me.com>,
		Denis Djubajlo <stdedjub@googlemail.com>,
		J.R. Oldroyd <fbsd@opal.com>,
		Mikaël Urankar <mikael.urankar@gmail.com>,
		Pierre-Emmanuel Pédron <pepcitron@gmail.com>,
		Sam Fourman Jr. <sfourman@gmail.com>,
		Wade <wade-is-great@live.com>,
		(probably other I forgot...)
HW donations:	kyzh, Yakaz
Bump __FreeBSD_version to 1000051 after Radeon KMS driver import