sched/fair: Prevent false-positive lockdep warnings

Below warnings are observed during boot when lockdep is enabled
due to double_lock_balance usage. Fix the warnings by disabling lockdep
checks before double_lock_balance call and enable it after
double_unlock_balance call.

[    0.180233] ------------[ cut here ]------------
[    0.180241] releasing a pinned lock
[    0.180271] WARNING: CPU: 0 PID: 17 at kernel/locking/lockdep.c:3676 \
						lock_release+0x30c/0x328
[    0.181279] Call trace:
[    0.181286]  lock_release+0x30c/0x328
[    0.181298]  _raw_spin_unlock+0x28/0x60
[    0.181307]  detach_task+0x74/0x130
[    0.181316]  active_load_balance_cpu_stop+0x48c/0x520
[    0.181327]  cpu_stopper_thread+0xac/0x150
[    0.181337]  smpboot_thread_fn+0x1c8/0x2e8
[    0.181346]  kthread+0x11c/0x130
[    0.181356]  ret_from_fork+0x10/0x1c
[    0.181447] ------------[ cut here ]------------
[    0.181453] unpinning an unpinned lock
[    0.181467] WARNING: CPU: 0 PID: 17 at kernel/locking/lockdep.c:3791 \
						lock_unpin_lock+0xcc/0xf0
[    0.182453] Call trace:
[    0.182460]  lock_unpin_lock+0xcc/0xf0
[    0.182468]  active_load_balance_cpu_stop+0x288/0x520
[    0.182475]  cpu_stopper_thread+0xac/0x150
[    0.182482]  smpboot_thread_fn+0x1c8/0x2e8
[    0.182488]  kthread+0x11c/0x130
[    0.182495]  ret_from_fork+0x10/0x1c.

Change-Id: I8113e7f7d01d2e84609e35563b507aea90236e70
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>