xa: add XA state tracker based EXA

Currently just for solid fills and blits (no composite wired up yet),
but this is enough to accelerate presentation blit (and avoid stalling
for GPU to complete and memcpy), which is pretty important for
performance of post-sub-buffer (gnome-shell and window managers),
windowed GL apps (including gpu based video rendering), etc.
add NoAccel config file option

Signed-off-by: Rob Clark <robdclark@gmail.com>
add man page with .conf file options

Signed-off-by: Rob Clark <robdclark@gmail.com>
Add option to disable SW_REFRESHER (KGSL)

Signed-off-by: Rob Clark <robdclark@gmail.com>
WIP: xa: add composite