dt-bindings: net: renesas,ethertsn: Add Ethernet TSN

Add bindings for Renesas R-Car Ethernet TSN End-station IP. The RTSN
device provides Ethernet network.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231121183738.656192-1-niklas.soderlund+renesas@ragnatech.se


Signed-off-by: Paolo Abeni <pabeni@redhat.com>