[SCSI] fc_transport: add target driver support

This adds minimum target driver support like the srp transport does:

- fc_remote_port_{rolechg,delete} calls
scsi_tgt_it_nexus_{create,destroy} for target drivers.

- add callbacks to notify target drivers of the nexus and tmf
operation results to fc_function_template.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>