Bluetooth: Controller: Add ASSERT info dump on HCI builds

When building Zephyr in the controller-only configuration,
assertions that happen in the Link Layer code are not visible
to the Host which is running on another HCI and connected via
UART or USB to it. This patch allows the Controller code
to output the assertion line number when in such a configuration,
allowing the Host to view the event to help debugging.

The event format used is temporary and will be replaced by a
standardized Vendor Specific specification to come at a later
time.

Change-Id: I013ca6783a3fdedc47b171132919dd4798c66285
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>