BugLink: https://launchpad.net/bugs/1625232

X-Gene mailbox controller provides 8 mailbox channels, with
each channel has a dedicated interrupt line.
Signed-off-by: Feng Kan <fkan@apm.com>
Signed-off-by: Duc Dang <dhdang@apm.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
(cherry picked from commit f700e84f)
Signed-off-by: Craig Magina <craig.magina@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>