rcu: Trace expedited grace-period numbers in hexadecimal

This commit reformats the expedited grace-period numbers into hexadecimal
for easier decoding and comparison.  The normal grace-period numbers
remain in decimal for the time being.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>