Bluetooth: Support HCI_QUIRK_EXTERNAL_CONFIG for hci_vhci driver

This adds support for configuring the hci_vhci virtual controllers
to require a setup stage using HCI_QUIRK_EXTERNAL_CONFIG. With this
option the virtual controller will start out as unconfigured.

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