drm/ingenic: Move IPU scale settings to private state

The IPU scaling information is computed in the plane's ".atomic_check"
callback, and used in the ".atomic_update" callback. As such, it is
state-specific, and should be moved to a private state structure.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20211026181240.213806-4-paul@crapouillou.net


Tested-by: Nikolaus Schaller <hns@goldelico.com>
Reviewed-by: Christophe Branchereau <cbranchereau@gmail.com>