drm/vc4: hdmi: Add audio-related callbacks

The audio configuration has changed for the BCM2711, with notably a
different parent clock and a different channel configuration.

Make that modular to be able to support the BCM2711.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
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>
Link: https://patchwork.freedesktop.org/patch/msgid/85a8ca721c2d800be758c55870cea98536749680.1599120059.git-series.maxime@cerno.tech