arm64: dts: meson: sei510: add sound card

arm64: dts: meson: sei510: add sound card

Enable the sound card on the sei510:
* TDM interface A is connected to an external DAC and a speaker installed
  on the device.
* HDMI is expected to use TDM B. It can also use TDM A but will be
  limited to 2 channels, as accepted by the external DAC.
* 2 Built in PDM mics through the PDM interface.
* Both TDM outputs may use HW loopback.

The internal DAC connected to audio jack will be added later on, when
driver support is added.

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