rwsem-spinlock: remove useless function exports

These functions need not to be exported, since no drivers should use them.

__init_rwsem() is an exception, because init_rwsem(), which is a macro,
is used.

Signed-off-by: WANG Cong <amwang@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>