MFC r248226:
  r241438 broke IPMI access on Sun Fire X2200 M2(BCM5715).
  Fix the IPMI regression by sending BGE_FW_DRV_STATE_UNLOAD to
  ASF/IPMI firmware in driver attach phase.  Sending heartheat to
  ASF/IPMI is enabled only after upping interface so
  setting driver state to BGE_FW_DRV_STATE_START in attach phase
  broke IPMI access.
  While I'm here, add NVRAM arbitration lock before performing
  controller reset. ASF/IPMI firmware may be able to access the NVRAM
  while controller reset is in progress.  Without the arbitration
  lock before resetting the controller, ASF/IPMI may not initialize
  properly.