Bluetooth: Mesh: Add composition data page 128

Composition data page 128 represents the new composition data after a
composition refresh procedure. The implementation stores the old
composition data (before applying a DFU or similar), and uses that as
page 0 if present. As the device has already rebooted by the time page
128 becomes active, its active composition data is page 128, while the
backed up data is the "old" data, which should be shown as page 0.

Co-authored-by: Ingar Kulbrandstad <ingar.kulbrandstad@nordicsemi.no>
Signed-off-by: Trond Einar Snekvik <Trond.Einar.Snekvik@nordicsemi.no>
Signed-off-by: Pavel Vasilyev <pavel.vasilyev@nordicsemi.no>