lsm: create new security_cred_getlsmprop LSM hook

lsm: create new security_cred_getlsmprop LSM hook

Create a new LSM hook security_cred_getlsmprop() which, like
security_cred_getsecid(), fetches LSM specific attributes from the
cred structure.  The associated data elements in the audit sub-system
are changed from a secid to a lsm_prop to accommodate multiple possible
LSM audit users.

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: subj line tweak]
Signed-off-by: Paul Moore <paul@paul-moore.com>