Bluetooth: Add driver setup stage for early init

Some drivers require a special stage for their early init. This is
always specific to the driver or transport. So call back into driver to
allow bringing up the device.

The advantage with this stage is that the Bluetooth core is actually
handling the HCI layer now. This means that command and event processing
is available.

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