When a plane moves out of bounds (i.e, outside the crtc clip region), the
plane state's "visible" parameter changes to false. When this happens, we
(a) release the hwpipe resources away from it, and
(b) unstage the corresponding hwpipe(s) from the Layer Mixers in the CRTC.

(a) requires use to acquire the global atomic state and assign a new
hwpipe. (b) requires us to re-configure the Layer Mixer, which is done in
the CRTC. We don't want to do these things in the async plane update path,
so return an error if the new state's "visible" isn't the same as the
current state's "visible".

Cc: Gustavo Padovan <gustavo.padovan@collabora.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>