arm64: dts: meson: gxl: add acodec support

Add the internal audio DAC to the gxl SoC DT

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20200506221656.477379-2-jbrunet@baylibre.com