clk: meson: axg: add the audio clock controller driver

The axg audio clock controller is the clock generation unit for the
amlogic audio subsystem of A113 based SoCs. It may be clocked by 8
different plls provided by the primary clock controller and also by
10 slave bit clocks and 10 slave sample clocks which may be provided
by external components, such as audio codecs, through the SoC pads.

It contains several muxes, dividers and gates which are fed into the
the different devices of the audio subsystem.

Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>