arm64: dts: meson-axg: add audio fifos

Add TODDR and FRDDR audio fifos of the AXG SoC.
These fifos are the capture and playback memory interfaces of audio
subsystem of the AXG.

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