Restore SignalTileView in CellularTile

When CellTileView was removed as it was not longer needed, this tile
lost its SignalTileView. It should have been made to create an instance
of SignalTileView instead of TileView.

Test: manual
Bug: 137614757
Change-Id: I9df951e97d7908c018aafb3d175fa557078aedcf