target: export lio pgr/alua support as device attr

Older kernels could crash or hang if the user write/read some ALUA files
with pscsi and tcmu backends. This patch exports if LIO supports
executing PGR and ALUA scsi commands/checks for the se_device, so userspace
can easily test.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>