Fix a WARN_ON caused by smp_call_function_any() when irq is disabled,
because of changes made in the patch ('cpufreq: powernv: Ramp-down
 global pstate slower than local-pstate')
https://patchwork.ozlabs.org/patch/612058/

 WARNING: CPU: 0 PID: 4 at kernel/smp.c:291
smp_call_function_single+0x170/0x180

 Call Trace:
 [c0000007f648f9f0] [c0000007f648fa90] 0xc0000007f648fa90 (unreliable)
 [c0000007f648fa30] [c0000000001430e0] smp_call_function_any+0x170/0x1c0
 [c0000007f648fa90] [c0000000007b4b00]
powernv_cpufreq_target_index+0xe0/0x250
 [c0000007f648fb00] [c0000000007ac9dc]
__cpufreq_driver_target+0x20c/0x3d0
 [c0000007f648fbc0] [c0000000007b1b4c] od_dbs_timer+0xcc/0x260
 [c0000007f648fc10] [c0000000007b3024] dbs_work_handler+0x54/0xa0
 [c0000007f648fc50] [c0000000000c49a8] process_one_work+0x1d8/0x590
 [c0000007f648fce0] [c0000000000c4e08] worker_thread+0xa8/0x660
 [c0000007f648fd80] [c0000000000cca88] kthread+0x108/0x130
 [c0000007f648fe30] [c0000000000095e8] ret_from_kernel_thread+0x5c/0x74

- Calling smp_call_function_any() with interrupt disabled (through
 spin_lock_irqsave) could cause a deadlock, as smp_call_function_any()
 relies on the IPI to complete. This is detected in the
 smp_call_function_any() call and hence the WARN_ON.

- As the spinlock (gpstates->lock) is only used to synchronize access of
 global_pstate_info  between timer irq handler and target_index calls. And
 the timer irq handler just try_locks() hence it would not cause a
 deadlock. Hence could do without making spinlocks irq safe.

- As the smp_call_function_any() is a blocking call and does not access
 global_pstates_info, it could reduce the critcal section by moving
 smp_call_function_any() after giving up the lock.
Reported-by: Abdul Haleem <abdhalee@linux.vnet.linux.com>
Signed-off-by: Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>