[SCSI] fcoe: removes phys_dev and renames real_dev to netdev.

The phys_dev was used only to locate common offload EM instance for all
FCoE instances on a eth devices in function fcoe_em_config, so just updated
fcoe_em_config to look for actual real eth device in locating common offload
EM instance and then no need to store phys_dev in fcoe_softc, so removes
phys_dev from fcoe_softc also.

Renames fcoe_softc real_dev to netdev and updates all its uses to use netdev.

So effectively no functional change, use of single netdev instead phys_dev
and real_dev saves one pointer memory in fcoe_softc, also real_dev used here
was confusing with vlan driver terminology since real_dev in vlan driver is
referred to physical eth device.

Signed-off-by: Vasu Dev <vasu.dev@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>