sched,psci: Convert to sched_set_fifo*()

Because SCHED_FIFO is a broken scheduler model (see previous patches)
take away the priority field, the kernel can't possibly make an
informed decision.

Effectively changes prio from 99 to 50.

XXX this thing is horrific, it basically open-codes a stop-machine and
idle.

Cc: daniel.lezcano@linaro.org
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/psci/psci_checker.c

@@ -272,7 +272,6 @@ static int suspend_test_thread(void *arg)
 {
 	int cpu = (long)arg;
 	int i, nb_suspend = 0, nb_shallow_sleep = 0, nb_err = 0;
-	struct sched_param sched_priority = { .sched_priority = MAX_RT_PRIO-1 };
 	struct cpuidle_device *dev;
 	struct cpuidle_driver *drv;
 	/* No need for an actual callback, we just want to wake up the CPU. */
@@ -282,9 +281,8 @@ static int suspend_test_thread(void *arg)
 	wait_for_completion(&suspend_threads_started);
 
 	/* Set maximum priority to preempt all other threads on this CPU. */
-	if (sched_setscheduler_nocheck(current, SCHED_FIFO, &sched_priority))
-		pr_warn("Failed to set suspend thread scheduler on CPU %d\n",
-			cpu);
+	if (sched_set_fifo(current))
+		pr_warn("Failed to set suspend thread scheduler on CPU %d\n", cpu);
 
 	dev = this_cpu_read(cpuidle_devices);
 	drv = cpuidle_get_cpu_driver(dev);
@@ -349,11 +347,6 @@ static int suspend_test_thread(void *arg)
 	if (atomic_dec_return_relaxed(&nb_active_threads) == 0)
 		complete(&suspend_threads_done);
 
-	/* Give up on RT scheduling and wait for termination. */
-	sched_priority.sched_priority = 0;
-	if (sched_setscheduler_nocheck(current, SCHED_NORMAL, &sched_priority))
-		pr_warn("Failed to set suspend thread scheduler on CPU %d\n",
-			cpu);
 	for (;;) {
 		/* Needs to be set first to avoid missing a wakeup. */
 		set_current_state(TASK_INTERRUPTIBLE);