doc: Update rcubarrier.rst

This commit updates rcubarrier.txt to reflect RCU additions and changes
over the past few years.

[ paulmck: Apply Stephen Rothwell feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2022-11-04 11:44:45 -07:00
commit 42d689ec00