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 cleans up hci_cmd_handle() to use the new macros
added in previous commits.
This is the fifth commit in a series that transitions from
the structures in hci.c to the ones in hci.h.

Jira: ZEP-726

Change-Id: I152e02ed15042d367e95432bdd07ae5c74935be8
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>