Bluetooth: btbcm: Add default address for BCM2076B1

BCM2076B1 appears to use 20:76:A0:00:56:79 as default address.
This address is used by at least 5 devices with the AMPAK AP6476
module and is also suspicious because it starts with the chip name
2076 (followed by a different revision A0 for some reason).

Add it to the list of default addresses and leave it up to the
user to configure a valid one.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>