MFC r257702, r257745, r257746, r257747, r257751, r257791, r257793,

MFC r257702, r257745, r257746, r257747, r257751, r257791, r257793,
    r257794, r257795, r257992

  Teach nexus(4) about Open Firmware (e.g. FDT) on ARM and MIPS, retiring
  fdtbus in most cases.

  Make OF_nextprop() work correctly for FDT by using the libfdt
  fdt_next_property_offset() API.

  Do not panic if pmap_mincore() is called.

  An addendum: it is possible, though of questionable utility, for a node
  to have no properties at all.
  Add definition for the Atheros 8021 gigabit PHY.

  Consolidate Apple firmware hacks and improve them by switching on the
  presence of mac-io devices in the tree, which uniquely identifies Apple
  hardware.

  Allow OF_decode_addr() to also be able to map resources on big-endian
  devices.

  Make tsec work with the device tree present on the RB800.

  Be more flexible about which compatible strings to accept.  This brings up
  the PCI Express bus on the RB800 using the firmware device tree.

  Rename the "bare" platform "mpc85xx", which is what it actually is, and
  add actual platform probing based on PVR.

git-svn-id: svn://svn.freebsd.org/base/stable/10@266000 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f