dt-bindings: net: wireless: Convert ESP ESP8089 binding to a schema

The ESP8089 Wireless Chip is supported by Linux (through an out-of-tree
driver) thanks to its device tree binding.

Now that we have the DT validation in place, let's convert the device
tree bindings for that driver over to a YAML schema.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: de Goede <hdegoede@redhat.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210924072756.869731-4-maxime@cerno.tech