Bluetooth: btbcm: Introduce generic Broadcom Bluetooth support

The majority of Broadcom Bluetooth vendor commands are shared between
USB and UART transports. This creates a separate module that eventually
will hold all Broadcom specific commands, but for now just start with
the commands to change the Bluetooth public address and check for the
default address.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>