rcu: Fold rcu_eqs_enter_common() into rcu_eqs_enter()

There is now only one call to rcu_eqs_enter_common() and there is no other
reason to keep it separate.  This commit therefore inlines it into its
sole call site, saving a few lines of code in the process.

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