gianfar: Pack struct gfar_priv_grp into three cachelines

* remove unused members(!): imask, ievent
* move space consuming interrupt name strings (int_name_* members) to
external structures, unessential for the driver's hot path
* keep high priority hot path data within the first 2 cache lines

This reduces struct gfar_priv_grp from 6 to 3 cache lines.
(Also fixed checkpatch warnings for the old code, in the process.)

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