dt-bindings: net: bluetooth: Add device tree bindings for QTI chip WCN3998

Add compatible string for the Qualcomm WCN3998 Bluetooth controller

Signed-off-by: Harish Bandi <c-hbandi@codeaurora.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>