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

Pull mailbox updates from Jassi Brar:

 - new driver for Broadcom FlexRM controller

 - constify data structures of callback functions in some drivers

 - a few bug fixes uncovered by multi-threaded use of mailbox channels
   in blocking mode

* 'mailbox-for-next' of git://git.linaro.org/landing-teams/working/fujitsu/integration:
  mailbox: handle empty message in tx_tick
  mailbox: skip complete wait event if timer expired
  mailbox: always wait in mbox_send_message for blocking Tx mode
  mailbox: Remove depends on COMPILE_TEST for BCM_FLEXRM_MBOX
  mailbox: check ->last_tx_done for NULL in case of timer-based polling
  dt-bindings: Add DT bindings info for FlexRM ring manager
  mailbox: Add driver for Broadcom FlexRM ring manager
  dt-bindings: mailbox: Update doc with NSP PDC/mailbox support
  mailbox: bcm-pdc: Add Northstar Plus support to PDC driver
  mailbox: constify mbox_chan_ops structures