[SCSI] scsi_transport_srp: remove tgt dependencies

it's better to remove tgt dependencies in srp transport class since
most people want only initiator support.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>