dt-bindings: Add optional nvmem BD address bindings to ti,wlink-st

This adds optional nvmem consumer properties to the ti,wlink-st device tree
bindings to allow specifying the BD address.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>