condvar: Clean up condvar.h a bit

- Remove a typedef that has been unused for a long time.
- Remove a LOCORE guard.  MI headers like condvar.h don't need such a
  guard in general.
- Move a forward declaration into the _KERNEL block.
- Add a types.h include to make the file self-contained.

Reviewed by:	kib
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D43449

sys/sys/condvar.h

@@ -29,14 +29,6 @@
 #ifndef	_SYS_CONDVAR_H_
 #define	_SYS_CONDVAR_H_
 
-#ifndef	LOCORE
-#include <sys/queue.h>
-
-struct lock_object;
-struct thread;
-
-TAILQ_HEAD(cv_waitq, thread);
-
 /*
  * Condition variable.  The waiters count is protected by the mutex that
  * protects the condition; that is, the mutex that is passed to cv_wait*()
@@ -49,6 +41,10 @@ struct cv {
 };
 
 #ifdef _KERNEL
+#include <sys/types.h>
+
+struct lock_object;
+
 void	cv_init(struct cv *cvp, const char *desc);
 void	cv_destroy(struct cv *cvp);
 
@@ -85,5 +81,4 @@ void	cv_broadcastpri(struct cv *cvp, int pri);
 #define	cv_wmesg(cvp)		((cvp)->cv_description)
 
 #endif	/* _KERNEL */
-#endif	/* !LOCORE */
 #endif	/* _SYS_CONDVAR_H_ */