kms: copy old fb to new fb on modeset

Based on what is done in the other big desktop DDX's.. before the splash
screen drops master, copy out it's contents.  This enables a seemless
transition from splash screen to greeter.

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