dt-bindings: net: qualcomm: Add WCN3988

Add the compatible for the Bluetooth part of the Qualcomm WCN3988
chipset.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>