Add a new wait_on_bit_timeout() helper, basically the same as
wait_on_bit() except that it also takes a 'timeout' parameter.

All the building blocks like bit_wait_timeout() and
out_of_line_wait_on_bit_timeout() are already in place so the
addition is rather simple.
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: davem@davemloft.net
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1422616476-2917-2-git-send-email-johan.hedberg@gmail.comSigned-off-by: Ingo Molnar <mingo@kernel.org>