lsm: use lsm_prop in security_current_getsecid

Change the security_current_getsecid_subj() and
security_task_getsecid_obj() interfaces to fill in a lsm_prop structure
instead of a u32 secid.  Audit interfaces will need to collect all
possible security data for possible reporting.

Cc: linux-integrity@vger.kernel.org
Cc: audit@vger.kernel.org
Cc: selinux@vger.kernel.org
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
[PM: subject line tweak]
Signed-off-by: Paul Moore <paul@paul-moore.com>