sched: make plist a library facility

Ingo Molnar wrote:

> here's a new build failure with tip/sched/rt:
>
>   LD      .tmp_vmlinux1
> kernel/built-in.o: In function `set_curr_task_rt':
> sched.c:(.text+0x3675): undefined reference to `plist_del'
> kernel/built-in.o: In function `pick_next_task_rt':
> sched.c:(.text+0x37ce): undefined reference to `plist_del'
> kernel/built-in.o: In function `enqueue_pushable_task':
> sched.c:(.text+0x381c): undefined reference to `plist_del'

Eliminate the plist library kconfig and make it available
unconditionally.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched_rt.c

@@ -114,14 +114,23 @@ static void dequeue_pushable_task(struct rq *rq, struct task_struct *p)
 
 #else
 
+static inline void enqueue_pushable_task(struct rq *rq, struct task_struct *p)
+{
+}
+
+static inline void dequeue_pushable_task(struct rq *rq, struct task_struct *p)
+{
+}
+
 static inline
-void enqueue_pushable_task(struct rq *rq, struct task_struct *p) {}
+void inc_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
+{
+}
+
 static inline
-void dequeue_pushable_task(struct rq *rq, struct task_struct *p) {}
-static inline
-void inc_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq) {}
-static inline
-void dec_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq) {}
+void dec_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
+{
+}
 
 #endif /* CONFIG_SMP */