target: consolidate backend attribute implementations

target: consolidate backend attribute implementations

Orabug: 25791789

Provide a common sets of dev_attrib attributes for all devices using the
generic SPC/SBC parsers, and a second one with the minimal required read-only
attributes for passthrough devices.  The later is only used by pscsi for now,
but will be wired up for the full-passthrough TCMU use case as well.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
(cherry picked from commit 5873c4d157400ade4052e9d7b6259fa592e1ddbf)
Reviewed-by: Ethan Zhao <ethan.zhao@oracle.com>
Signed-off-by: Shan Hai <shan.hai@oracle.com>