dt-bindings: net: realtek-bluetooth: Add RTL8723DS

RTL8723DS is another variant of the RTL8723 WiFi + Bluetooth chip. It is
already supported by the hci_uart/btrtl driver. Document the compatible.

Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Alistair Francis <alistair@alistair23.me>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>