bluetooth: host: HCI support for CS configuration

Adds following HCI support for CS configuration:
- LE CS Create Config command
- LE CS Remove Config command
- LE CS Config Complete event

Two callbacks have been added to notify the application
when a new CS configuration is created or an existing
CS configuration is removed.

Signed-off-by: Burak Gorduk <burak.gorduk@nordicsemi.no>