Now that we have a helper to fill the plane state co-ordinates from a
view, use this for the scanout plane.

We now explicitly check that the view fills exactly the fullscreen area
and nothing else. We then use the new helper to fill out the plane state
values, and do further checks against the filled-in co-ordinates, i.e.
that we're not trying to show an offset into the buffer, or to scale the
image.

This now allows cases where the buffer -> surface -> view -> output
transform chain cancels each other out for scaling: previously, we would
never consider a buffer for scanout unless its scale matched the
output's. We now only look at the final result of the buffer -> output
transformation, to check that this does not result in translation or
scaling.

An audit of the error paths found some places where we would leave a
plane state hanging; this makes them all consistent.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Tested-by: Emre Ucan <eucan@de.adit-jv.com>