[SCSI] fcoe: Introduce and allocate fcoe_interface structure, 1:1 with net_device

In preparation for NPIV support, I'm splitting the fcoe instance structure
into two to remove the assumptions about it being 1:1 with the net_device.
There will now be two structures, one which is 1:1 with the underlying
net_device and one which is allocated per virtual SCSI/FC host.

fcoe_softc is renamed to fcoe_port for the per Scsi_Host FCoE private data.

Later patches with start moving shared stuff from fcoe_port to fcoe_interface

Signed-off-by: Chris Leech <christopher.leech@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>