Bluetooth: hci_uart: Add diag and address support for Intel/AG6xx

The AG6xx devices behave similar to Wilkens Peak and Stone Peak and with
that it is needed to check for Intel default address. In addition it is
possible to enable vendor events and diag support.

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