sched: Disable interrupts while holding related_thread_group_lock

There is a potential deadlock condition if interrupts are enabled
while holding the related_thread_group_lock. Prevent this.

----------------                              --------------------
    CPU 0                                          CPU 1
---------------                               --------------------

check_for_migration()                         cgroup_file_write(p)

check_for_freq_change()                       cgroup_attach_task(p)

send_notification()                           schedtune_attach(p)

read_lock(&related_thread_group_lock)         sched_set_group_id(p)

                                              raw_spin_lock_irqsave(
					       &p->pi_lock, flags)

					      write_lock_irqsave(
					       &related_thread_group_lock)

					       waiting on CPU#0

raw_spin_lock_irqsave(&rq->lock, flags)

raw_spin_unlock_irqrestore(&rq->lock, flags)

--> interrupt()

----> ttwu(p)

-------> waiting for p's pi_lock on CPU#1

Change-Id: I6f0f8f742d6e1b3ff735dcbeabd54ef101329cdf
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>