sched/headers: Only include <linux/entry-common.h> when CONFIG_GENERIC_ENTRY=y

This header is not (yet) standalone.
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -63,7 +63,9 @@
 #include <linux/workqueue_api.h>
 
 #ifdef CONFIG_PREEMPT_DYNAMIC
-# include <linux/entry-common.h>
+# ifdef CONFIG_GENERIC_ENTRY
+#  include <linux/entry-common.h>
+# endif
 #endif
 
 #include <uapi/linux/sched/types.h>