lsm: add the lsm_prop data structure

lsm: add the lsm_prop data structure

When more than one security module is exporting data to audit and
networking sub-systems a single 32 bit integer is no longer
sufficient to represent the data. Add a structure to be used instead.

The lsm_prop structure definition is intended to keep the LSM
specific information private to the individual security modules.
The module specific information is included in a new set of
header files under include/lsm. Each security module is allowed
to define the information included for its use in the lsm_prop.
SELinux includes a u32 secid. Smack includes a pointer into its
global label list. The conditional compilation based on feature
inclusion is contained in the include/lsm files.

Cc: apparmor@lists.ubuntu.com
Cc: bpf@vger.kernel.org
Cc: selinux@vger.kernel.org
Cc: linux-security-module@vger.kernel.org
Suggested-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: John Johansen <john.johansen@canonical.com>
[PM: added include/linux/lsm/ to MAINTAINERS, subj tweak]
Signed-off-by: Paul Moore <paul@paul-moore.com>