[SCSI] fcoe: Move common functions to fcoe_transport library

Export fcoe_get_wwn, fcoe_validate_vport_create and fcoe_wwn_to_str so that all
LLDs can use these common function.

Signed-off-by: Bhanu Prakash Gollapudi <bprakash@broadcom.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>