Bluetooth: Mesh: Enable CDP1 by default

CDP1 is mandatory to qualify a mesh device for mesh protocol v1.1.
The dependency on BT_MESH_MODEL_EXTENSIONS is removed because if a node
contains only base models (for example Generic OnOff Server), this API
will consume extra RAM bytes which won't be used.

Signed-off-by: Pavel Vasilyev <pavel.vasilyev@nordicsemi.no>