staging: fsl-dpaa2/eth: add ETHERNET dependency

The new driver cannot link correctly when the netdevice infrastructure
is disabled:

ERROR: "netdev_info" [drivers/staging/fsl-dpaa2/ethernet/fsl-dpaa2-eth.ko] undefined!
ERROR: "skb_to_sgvec" [drivers/staging/fsl-dpaa2/ethernet/fsl-dpaa2-eth.ko] undefined!
ERROR: "napi_disable" [drivers/staging/fsl-dpaa2/ethernet/fsl-dpaa2-eth.ko] undefined!
ERROR: "napi_schedule_prep" [drivers/staging/fsl-dpaa2/ethernet/fsl-dpaa2-eth.ko] undefined!
ERROR: "__napi_schedule_irqoff" [drivers/staging/fsl-dpaa2/ethernet/fsl-dpaa2-eth.ko] undefined!
ERROR: "netif_carrier_on" [drivers/staging/fsl-dpaa2/ethernet/fsl-dpaa2-eth.ko] undefined!

This adds a dependency on NETDEVICES and ETHERNET.

Fixes: 0352d1d8 ("staging: fsl-dpaa2/eth: Add APIs for DPNI objects")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>