iSCSILogicalUnit: lio-t: support setting product_id

Since Linux kernel commit 0322913cab79 ("scsi: target: Add device
product id and revision configfs attributes"), setting a SCSI product id
via the product_id configfs attribute is supported in the target
subsystem.

Thus, forward the value of the product_id resource agent parameter there
and remove it from the list of unsupported parameters for lio-t.