Bluetooth: Controller: Use hci.h for control event handling

Use Zephyr's include/bluetooth/hci.h for HCI event
handling in control events.
This is the first commit in a series that transitions from
the event structures in hci.c to the ones in hci.h.

Jira: ZEP-726

Change-Id: I6f131675add18e2ae061f0fb2cf220ea7057f852
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>