Introduction of __smp barriers cleans up a bunch of duplicate code, but
it gives people an additional handle onto a "new" set of barriers - just
because they're prefixed with __* unfortunately doesn't stop anyone from
using it (as happened with other arch stuff before.)

Add a checkpatch test so it will trigger a warning.
Reported-by: NRussell King <linux@arm.linux.org.uk>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Acked-by: NJulian Calaby <julian.calaby@gmail.com>
Acked-by: NJoe Perches <joe@perches.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>