selinux: add permission checks for loading other kinds of kernel files

Although the LSM hooks for loading kernel modules were later generalized
to cover loading other kinds of files, SELinux didn't implement
corresponding permission checks, leaving only the module case covered.
Define and add new permission checks for these other cases.

Signed-off-by: Cameron K. Williams <ckwilliams.work@gmail.com>
Signed-off-by: Kipp N. Davis <kippndavis.work@gmx.com>
Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>
[PM: merge fuzz, line length, and spacing fixes]
Signed-off-by: Paul Moore <paul@paul-moore.com>