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>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Tested-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://patchwork.freedesktop.org/patch/msgid/71cfa3ce3d865bbab52a0e5651bc052dc4893f11.1599120059.git-series.maxime@cerno.tech