drm/vc4: hdmi: Introduce resource init and variant

The HDMI controllers found in the BCM2711 has a pretty different clock and
registers areas than found in the older BCM283x SoCs.

Let's create a variant structure to store the various adjustments we'll
need later on, and a function to get the resources needed for one
particular version.

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