As discussed, clarify LKMM not recognizing certain kinds of orderings.
In particular, highlight the fact that LKMM might deliberately make
weaker guarantees than compilers and architectures.

[ paulmck: Fix whitespace issue noted by checkpatch.pl. ]

Link: https://lore.kernel.org/all/YpoW1deb%2FQeeszO1@ethstick13.dse.in.tum.de/T/#uCo-developed-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NPaul Heidekrüger <paul.heidekrueger@in.tum.de>
Reviewed-by: NMarco Elver <elver@google.com>
Reviewed-by: NJoel Fernandes (Google) <joel@joelfernandes.org>
Cc: Charalampos Mainas <charalampos.mainas@gmail.com>
Cc: Pramod Bhatotia <pramod.bhatotia@in.tum.de>
Cc: Soham Chakraborty <s.s.chakraborty@tudelft.nl>
Cc: Martin Fink <martin.fink@in.tum.de>
Signed-off-by: NPaul E. McKenney <paulmck@kernel.org>