liblockdep: Add public headers for pthread_rwlock_t implementation

Both pthreads and lockdep support dealing with rwlocks, so
here's the liblockdep implementation for those.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: torvalds@linux-foundation.org
Link: http://lkml.kernel.org/r/1371163284-6346-6-git-send-email-sasha.levin@oracle.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>