freedreno: add freedreno DRM

The libdrm_freedreno helper layer for use by xf86-video-freedreno,
fdre (freedreno r/e library and tests for driving gpu), and eventual
gallium driver for the Adreno GPU.  This uses the msm gpu driver
from QCOM's android kernel tree.

Note that current msm kernel driver is a bit strange.  It provides a
DRM interface for GEM, which is basically sufficient to have DRI2
working.  But it does not provide KMS.  And interface to 2d and 3d
cores is via different other devices (/dev/kgsl-*).  This is not
quite how I'd write a DRM driver, but at this stage it is useful for
xf86-video-freedreno and fdre (and eventual gallium driver) to be
able to work on existing kernel driver from QCOM, to allow to
capture cmdstream dumps from the binary blob drivers without having
to reboot.  So libdrm_freedreno attempts to hide most of the crazy.
The intention is that when there is a proper kernel driver, it will
be mostly just changes in libdrm_freedreno to adapt the gallium
driver and xf86-video-freedreno (ignoring the fbdev->KMS changes).

So don't look at freedreno as an example of how to write a libdrm
module or a DRM driver.. it is just an attempt to paper over a non-
standard kernel driver architecture.

v1: original
v2: hold ref's to pending bo's (because qcom's kernel driver doesn't),
    various bug fixes, add ringbuffer markers so we can emit IB's to
    portion of ringbuffer (so that gallium driver can use a single
    ringbuffer for both tile cmds and draw cmds.

Signed-off-by: Rob Clark <robclark@freedesktop.org>