freedreno: Add a6xx backend

This adds a freedreno backend for the a6xx generation GPUs, which at
the time of this commit is about 98% GLES2 conformant. Much remains to
be done - both performance work and feature work towards more recent
GLES versions, but this is a good start.

Signed-off-by: Kristian H. Kristensen <hoegsberg@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>
40 files changed