[POWERPC] QE: UCC nodes cleanup

[POWERPC] QE: UCC nodes cleanup

- get rid of `model = "UCC"' in the ucc nodes
  It isn't used anywhere, so remove it. If we'll ever need something
  like this, we'll use compatible property instead.
- replace last occurrences of device-id with cell-index.
  Drivers are modified for backward compatibility's sake.

Signed-off-by: Anton Vorontsov <[email protected]>
Acked-by: Timur Tabi <[email protected]>
Signed-off-by: Kumar Gala <[email protected]>