ASoC: meson: axg-fifo: add g12a support

The g12a fifos gained the ability to set the initial address of the
pointer within the buffer, instead of defaulting to the buffer start
address.

It is not very useful to us (yet) but we need to put a copy the buffer
start address in the related register for the fifo to work properly on the
g12a SoC family

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Mark Brown <broonie@kernel.org>