Pull mailbox updates from Jassi Brar:
 "Change to POLL api and fixes for FlexRM and OMAP driver.

  Summary:

   - Core: Prefer ACK method over POLL, if both supported

   - Test: use flag instead of special character

   - FlexRM: Usual driver internal minor churn

   - Omap: fix error path"

* tag 'mailbox-v4.15' of git://git.linaro.org/landing-teams/working/fujitsu/integration:
  mailbox/omap: unregister mbox class
  mailbox: mailbox-test: don't rely on rx_buffer content to signal data ready
  mailbox: reset txdone_method TXDONE_BY_POLL if client knows_txdone
  mailbox: Build Broadcom FlexRM driver as loadable module for iProc SOCs
  mailbox: bcm-flexrm-mailbox: Use common GPL comment header
  mailbox: bcm-flexrm-mailbox: add depends on ARCH_BCM_IPROC
  mailbox: bcm-flexrm-mailbox: Print ring number in errors and warnings
  mailbox: bcm-flexrm-mailbox: Fix FlexRM ring flush sequence