Make kernel / init enforcing

Start running in enforcing mode for kernel / init.
This should be mostly a no-op, as the kernel / init
is in the unconfined domain.

Change-Id: I8273d936c9a4eecb50b78ae93490a4dd52f59eb6

init.te

 # init switches to init domain (via init.rc).
 type init, domain;
-permissive init;
 # init is unconfined.
 unconfined_domain(init)
 tmpfs_domain(init)

kernel.te

 # Life begins with the kernel.
 type kernel, domain;
-permissive kernel;
 # The kernel is unconfined.
 unconfined_domain(kernel)
 relabelto_domain(kernel)