drm/vc4: Pass the atomic state to encoder hooks

We'll need to access the connector state in our encoder setup, so let's
just pass the whole DRM state to our private encoder hooks.

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20201215154243.540115-3-maxime@cerno.tech