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

Pull mailbox framework updates from Jassi Brar.

* 'mailbox-devel' of git://git.linaro.org/landing-teams/working/fujitsu/integration:
  Mailbox: Add support for Platform Communication Channel
  mailbox/omap: adapt to the new mailbox framework
  mailbox: add tx_prepare client callback
  mailbox: Don't unnecessarily re-arm the polling timer