sched/fair: Add timeout for detach_tasks() in load balance

When the busy CPU has thousands of tasks, the current loop break
of 32 does not scale nicely. Because each task deactivation may
take ~5 msec. Since this all happens from interrupts disabled
(from softirq also), it is resulting in watchdog bark. Hence
add 5 msec timeout in detach_tasks() to abort the load balance.

Change-Id: I290f75076f13a44d866dc4fe5fe6653733d28fbc
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>