lsm: Add/fix return values in lsm_hooks.h and fix formatting

Ensure that for non-void LSM hooks there is a description of the return
values.

Also, replace spaces with tab for indentation, remove empty lines between
the hook description and the list of parameters, adjust semicolons and add
the period at the end of the parameter description.

Finally, move the description of gfp parameter of the
xfrm_policy_alloc_security hook together with the others.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
[PM: /replaces./replaced./]
Signed-off-by: Paul Moore <paul@paul-moore.com>