ARM64: dts: meson-axg: add the audio clock controller

Add the audio clock controller which is part of the audio bus
This controller takes 8 input plls, and the usual clock gate, from the
main clock controller. It provides the clocs for the all the devices of
the audio subsystem, such as tdms, spdif, pdm, etc.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>