driver: netdev: cc2420: Move radio_driver to netdev_802154 & Port cc2420 accordingly

Test with 

```
export BOARD=telosb # or z1, or wsn430-v1_4
SENDER=0 make -C tests/netdev/ all flash && SENDER=1 make -C tests/netdev/ all flash && make -C tests/netdev/ test
```

Depends on #1492.

```
* #1733
| * #1732
|/
| * #1731
|/
* #1492
```