clk: meson: axg-audio: separate axg and g12a regmap tables

There are more differences than what we initially thought.
Let's keeps things clear and separate the axg and g12a regmap tables of the
audio clock controller.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20200729154359.1983085-3-jbrunet@baylibre.com