Bluetooth: Mesh: Support for comp data page 2

Adds support for composition data page 2 & 130.

In this implementation the responsibillity for filling the page 2
buffer is left to the application through the new comp page 2 cb API.
Only the application can know/decide if the device is NLC compliant,
and must thus be given the responsibillity for cheking the NLC profile
requirements, defined in the NLC specs, and filling the response buffer
for comp data page 2.

Signed-off-by: Anders Storrø <anders.storro@nordicsemi.no>