locktorture: Add acq_writer_lim to complain about long acquistion times

This commit adds a locktorture.acq_writer_lim module parameter that
specifies the maximum number of jiffies that is expected to be consumed
by write-side lock acquisition.  If this limit is exceeded, a WARN_ONCE()
causes a splat.  Note that this limit applies to the main lock acquisition
only, not to any nested acquisitions.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>