Bluetooth: Add mgmt_device_found event

This patch adds a device_found event to the Management interface. For
now the event only maps to BR/EDR inquiry result HCI events, but in the
future the plan is to also use it for the LE device discovery process.

Signed-off-by: Johan Hedberg <johan.hedberg@nokia.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>