drm/vc4: Switch to container_of_const

container_of_const() allows to preserve the pointer constness and is
thus more flexible than inline functions.

Let's switch all our instances of container_of() to
container_of_const().

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/20221207-rpi-hdmi-improvements-v3-1-bdd54f66884e@cerno.tech


Signed-off-by: Maxime Ripard <maxime@cerno.tech>