rcu: Round FAST_NO_HZ lazy timeout to nearest second

Currently, if several CPUs in the same package have all lazy RCU
callbacks, their wakeups will be uncorrelated.  If all the CPUs are in the
same power domain (as is often the case), this will result in unnecessary
power-ups of the package.  This commit therefore uses round_jiffies()
to round the timeouts to a second boundary, increasing the odds that
they can be coalesced with each other or with other timeouts.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>