[SCSI] srp_transport: add target driver support

This adds minimum target driver support:

- srp_rport_{add,del} calls scsi_tgt_it_nexus_{create,destroy} for
target drivers.

- add a callback to notify target drivers of the nexus operation
results to srp_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>
diff --git a/drivers/scsi/Kconfig b/drivers/scsi/Kconfig
index 778dc0f..8d4057e 100644
--- a/drivers/scsi/Kconfig
+++ b/drivers/scsi/Kconfig
@@ -291,7 +291,7 @@
 
 config SCSI_SRP_ATTRS
 	tristate "SRP Transport Attributes"
-	depends on SCSI
+	depends on SCSI && SCSI_TGT
 	help
 	  If you wish to export transport-specific information about
 	  each attached SRP device to sysfs, say Y.