gianfar: Use ndev, more Rx path cleanup

Use "ndev" instead of "dev", as the rx queue back pointer
to a net_device struct, to avoid name clashing with a
"struct device" reference.  This prepares the addition of a
"struct device" back pointer to the rx queue structure.

Remove duplicated rxq registration in the process.
Move napi_gro_receive() outside gfar_process_frame().

Signed-off-by: Claudiu Manoil <claudiu.manoil@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>