Documentation,barriers: Mention smp_cond_acquire()

... do this next to smp_load_acquire when first mentioning
ACQUIRE. While this call is briefly explained and ctrl
dependencies are mentioned later, it does not hurt the reader.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
1 file changed