dt-bindings: soc: qcom: Add local-bd-address property to WCNSS-BT

Add optional local-bd-address property which is a 6-byte array
storing the assigned BD address. Since having a unique BD address
is critical, a per-device property value should be allocated.
This property is usually added by the boot loader which has access
to the provisioned data.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>