Fix some RCU problem pointed out by Paul McKenney of IBM.  These are:

The wholesale move of the command receivers list into a new list was not
safe because the list will point to the new tail during a traversal, so the
traversal will never end on a reader if this happens during a read.

Memory barriers were needed to handle proper ordering of the setting of the
IPMI interface as valid.  Readers might not see proper ordering of data
otherwise.

In ipmi_smi_watcher_register(), the use of the _rcu suffix on the list is
unnecessary.

This require the list_splice_init_rcu() patch previously posted.
Signed-off-by: Corey Minyard <minyard@acm.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>