cpuset: Move userspace declarations out of _cpuset.h

The _*.h headers are for structure definitions and should avoid
dependencies on other headers.  This convention is violated by using
__BEGIN_DECLS/__END_DECLS.

Move the declarations to cpuset.h, I see no reason they can't be there.

Reviewed by:	olce, brooks, kib
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D56856

sys/sys/_cpuset.h

@@ -49,11 +49,4 @@
 __BITSET_DEFINE(_cpuset, CPU_SETSIZE);
 typedef struct _cpuset cpuset_t;
 
-#ifndef _KERNEL
-__BEGIN_DECLS
-cpuset_t *__cpuset_alloc(size_t set_size);
-void __cpuset_free(cpuset_t *ptr);
-__END_DECLS
-#endif
-
 #endif /* !_SYS__CPUSET_H_ */

sys/sys/cpuset.h

@@ -181,8 +181,13 @@ int	cpusetobj_strscan(cpuset_t *, const char *);
 void	ddb_display_cpuset(const cpuset_t *);
 #endif
 
-#else
+#else /* !_KERNEL */
+#include <sys/cdefs.h>
+
 __BEGIN_DECLS
+cpuset_t *__cpuset_alloc(size_t set_size);
+void	__cpuset_free(cpuset_t *ptr);
+
 int	cpuset(cpusetid_t *);
 int	cpuset_setid(cpuwhich_t, id_t, cpusetid_t);
 int	cpuset_getid(cpulevel_t, cpuwhich_t, id_t, cpusetid_t *);