[MIPS] SELinux: Add security hooks to mips-mt {get,set}affinity

This patch adds LSM hooks into the setaffinity and getaffinity functions
for the mips architecture to enable security modules to control these
operations between tasks with different security attributes. This
implementation uses the existing task_setscheduler and task_getscheduler
LSM hooks.
    
Signed-Off-By: David Quigley <dpquigl@tycho.nsa.gov>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>