These comments are used by static code analysis tools and in code reviews
to avoid false warnings because of missing break statements.

The case statements handled here were reported by coverity.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>