MFC r256870, r256898, r256899, r256900 (by nwhitehorn):

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).

git-svn-id: svn://svn.freebsd.org/base/stable/10@265959 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f