workqueue: Split out workqueue_types.h

More sched.h dependency culling - this lets us kill a rhashtable-types.h
dependency on workqueue.h.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

include/linux/rhashtable-types.h

@@ -12,7 +12,7 @@
 #include <linux/atomic.h>
 #include <linux/compiler.h>
 #include <linux/mutex.h>
-#include <linux/workqueue.h>
+#include <linux/workqueue_types.h>
 
 struct rhash_head {
 	struct rhash_head __rcu		*next;