sched/cputime: Fix a deadlock on 32bit systems

CPU's irqtime structure updates are protected with a seqlock on
32bit systems. There is a potential deadlock with this seqlock
and rq->lock.

CPU 1                             CPU0
==========================        ========================
--> acquire CPU0 rq->lock         --> __irq_enter()
----> task enqueue/dequeue        ----> irqtime_account_irq()
------> update_rq_clock()         ------> u64_stats_update_begin()
--------> irq_time_read()         --------> sched_account_irqtime()
(waiting for the seqlock          (waiting for the CPU0 rq->lock)
held in u64_stats_update_begin()

Fix this issue by dropping the seqlock before calling
sched_account_irqtime().

Change-Id: I29a33876e372f99435a57cc11eada9c8cfd59a3f
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>