MFC r257111, r257144, r257157, r257183

  Test UARTs physical address instead of virtual.

  Be a bit more flexible in how we find the console from the properties on
  /chosen, following the list of allowed console properties in ePAPR. Also
  do not require that stdin be defined and equal to stdout: stdin is
  nonstandard (for ePAPR) and console in an unexpected place is after all
  better than no console.
MFC r257162, r257175

  The old trap.h (then trap_aim.h) actually had trap ID codes for Book-E CPUs.
  Use it universally. Book-E traps may also need revisiting due to the
  introduction of fixed-offset traps and the deprecation of IVORs in POWER
  ISA 2.06, but that's very much an issue for another day.