ANDROID: __migrate_task header

__migrate_task is used by modules to move tasks between cpus.
This function is needed by modules and is currently exported,
allowing it to be used.

As part of this, there was a change so this is no longer static.
This causes a warning, due to a missed extern available in the
scheduler header file.

Correct the issue to cleanup the warning, and properly reference
__migrate_task through the appropriate header file.

Bug: 205164003
Change-Id: Ifb194108cec34467315f43858ebeae428b2e34f0
Signed-off-by: Stephen Dickey <quic_dickey@quicinc.com>

kernel/sched/sched.h

@@ -1546,6 +1546,14 @@ struct rq_flags {
 #endif
 };
 
+#ifdef CONFIG_SMP
+extern struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
+				 struct task_struct *p, int dest_cpu);
+#else /* !CONFIG_SMP */
+static inline rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
+				 struct task_struct *p, int dest_cpu) { return rq; }
+#endif
+
 extern struct callback_head balance_push_callback;
 
 /*