dt-bindings: marvell: a38x: convert soc compatibles to yaml

Convert the existing txt binding for armada-38x socs to DT schema
format.

The current bindings documentation for armada-38x are only listing SoCs,
but no actual boards. Only actual boards should be listed.

Replace the dropped entries with some actual baords that already have
valid compatibles in-tree:
- armada 380 netgear switch
- armada 385 marvell development boards
- armada 388 development board

Signed-off-by: Josua Mayer <josua@solid-run.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>