sun4i/drm: engine: Add mode_set callback

This optional callback is useful for setting properties which depends
only on current mode. Such properties are width, height and interlaced
output.

These properties are currently set in update layer callback for primary
plane which is less than ideal. More about that in follow up patches,
which will migrate that code to this newly defined callback.

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220424162633.12369-7-samuel@sholland.org