Merge branch 'mailbox-for-next' of git://git.linaro.org/landing-teams/working/fujitsu/integration

Pull mailbox updates from Jassi Brar:

 - Minor improvement : avoid requiring unnecessary startup/shutdown
   callback that many drivers seem to not need

 - New controller driver for Qualcomm's APCS IPC

* 'mailbox-for-next' of git://git.linaro.org/landing-teams/working/fujitsu/integration:
  mailbox: Introduce Qualcomm APCS IPC driver
  dt-bindings: mailbox: Introduce Qualcomm APCS global binding
  mailbox: Make startup and shutdown ops optional