Bluetooth: Controller: Switch to Zephyr's hci.h for cmd handling

Continue using Zephyr's include/bluetooth/hci.h for HCI command
handling in more of the commands.
This commit deletes all command and command complete and
command status event definitions and structures present in
hci.c.
This is the sixth commit in a series that transitions from
the structures in hci.c to the ones in hci.h.

Jira: ZEP-726

Change-Id: I34635a1f55f3aef124fd5ff005c99cedb40b8a49
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>