accel: split out z1xx 2d core bits

Just cleaning up, separating out a bit better some of the 2d core parts.

Signed-off-by: Rob Clark <robdclark@gmail.com>
kms: fix crash with NoAccel

In that case, PrepareCopy will fail.  Don't care about it too much, just
go fallback path.

Signed-off-by: Rob Clark <robdclark@gmail.com>
kms: fix crash on startup with no display

We need to have *some* scanout buffer, even if it will be re-allocated
when a display is actually attached.

Signed-off-by: Rob Clark <robdclark@gmail.com>