MFC r256792, r256793, r256799 (by nwhitehorn): Unify AIM and booke code.
MFC r256798: Return BUS_PROBE_NOWILDCARD from fdtbus_probe.
MFC r256814, r256816, r256818, r256846, r256855, r256864 (by nwhitehorn):

 - Handle 2GB of ram
 - Allow the OFW interrupt mapping code to work with PCI devices not
   enumerated by Open Firmware, as in the case of FDT.
 - Provide an interface for PCI bus drivers that need some of ofw_pci's
   metadata during attach.
 - Use standard ofw_bus helpers instead of reinventing the wheel.
 - Make hard-wired TLB allocations be at minimum one page.
MFC r256870, r256898, r256899, r256900 (by nwhitehorn):

 Standards-conformance and code deduplication:
  - Use bus reference phandles in place of FDT offsets as IRQ domain keys
  - Unify the identical macio/fdt/mambo OpenPIC drivers into one
  - Be more forgiving (following ePAPR) about what we need from the device
    tree to identify an OpenPIC
  - Correctly map all IRQs into an interrupt domain
  - Set IRQ_*_CONFORM for interrupts on an unknown PIC type instead of
    failing attachment for that device.

  Allow lots of interrupts (useful on multi-domain platforms) and do not
  set device_quiet() on all devices attached under nexus(4).
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.