sched: Clean up and standardize #if/#else/#endif markers in sched/idle.c

- Use the standard #ifdef marker format for larger blocks,
   where appropriate:

        #if CONFIG_FOO
        ...
        #else /* !CONFIG_FOO: */
        ...
        #endif /* !CONFIG_FOO */

 - Fix whitespace noise and other inconsistencies.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20250528080924.2273858-11-mingo@kernel.org

kernel/sched/idle.c

@@ -52,7 +52,7 @@ static int __init cpu_idle_nopoll_setup(char *__unused)
 	return 1;
 }
 __setup("hlt", cpu_idle_nopoll_setup);
-#endif
+#endif /* CONFIG_GENERIC_IDLE_POLL_SETUP */
 
 static noinline int __cpuidle cpu_idle_poll(void)
 {
@@ -100,10 +100,10 @@ static inline void cond_tick_broadcast_exit(void)
 	if (static_branch_unlikely(&arch_needs_tick_broadcast))
 		tick_broadcast_exit();
 }
-#else
+#else /* !CONFIG_GENERIC_CLOCKEVENTS_BROADCAST_IDLE: */
 static inline void cond_tick_broadcast_enter(void) { }
 static inline void cond_tick_broadcast_exit(void) { }
-#endif
+#endif /* !CONFIG_GENERIC_CLOCKEVENTS_BROADCAST_IDLE */
 
 /**
  * default_idle_call - Default CPU idle routine.
@@ -444,7 +444,7 @@ balance_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 {
 	return WARN_ON_ONCE(1);
 }
-#endif
+#endif /* CONFIG_SMP */
 
 /*
  * Idle tasks are unconditionally rescheduled: