sched_ext: Collect ext_*.c include headers in build_policy.c

Move <linux/btf_ids.h> from ext.c and "ext_idle.h" from ext.c (plus its
self-include in ext_idle.c) into build_policy.c. Subsequent patches add
their headers the same way for consistency.

No functional change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

kernel/sched/build_policy.c

@@ -58,7 +58,9 @@
 #include "deadline.c"
 
 #ifdef CONFIG_SCHED_CLASS_EXT
+# include <linux/btf_ids.h>
 # include "ext_internal.h"
+# include "ext_idle.h"
 # include "ext.c"
 # include "ext_idle.c"
 #endif

kernel/sched/ext.c

@@ -6,8 +6,6 @@
  * Copyright (c) 2022 Tejun Heo <tj@kernel.org>
  * Copyright (c) 2022 David Vernet <dvernet@meta.com>
  */
-#include <linux/btf_ids.h>
-#include "ext_idle.h"
 
 static DEFINE_RAW_SPINLOCK(scx_sched_lock);
 

kernel/sched/ext_idle.c

@@ -9,7 +9,6 @@
  * Copyright (c) 2022 David Vernet <dvernet@meta.com>
  * Copyright (c) 2024 Andrea Righi <arighi@nvidia.com>
  */
-#include "ext_idle.h"
 
 /* Enable/disable built-in idle CPU selection policy */
 static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_enabled);