MFC r256901, r256914 (by nwhitehorn):

MFC r256901, r256914 (by nwhitehorn):

  Catch up on 6 years of improvements in Open Firmware nexus devices by
  importing the sparc64 one. At least 90% of this code is MI and will be
  moved into /sys/dev/ofw at some point in the future.

  Ignore registers on devices where the reg property is malformed. Issue a
  warning if this happens under bootverbose. This prevents some
  strange-looking entries in dmesg for SMU devices on Apple G5 systems.

git-svn-id: svn://svn.freebsd.org/base/stable/10@265960 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f