MFC r258800, r258802, r258805, r258806, r258807, r258851, r258857,

MFC r258800, r258802, r258805, r258806, r258807, r258851, r258857,
    r259199, r259484, r259513, r259514, r259516

  The kernel stack guard pages are only below the stack pointer, not above.

  Remove unnecessary double-setting of the thread's onfault state in
  copyinstr().

  Open Firmware mandates that certain cross-references, in particular those
  in /chosen, be ihandles. The ePAPR spec makes those cross-reference phandles,
  since FDT has no concept of ihandles. Have the OF FDT CI module interpret
  queries about ihandles as cross-reference phandles.

  Real OF systems have an ihandle under /chosen/stdout, not a phandle. Use
  the right type.

  Rearchitect platform memory map parsing to make it less
  Open Firmware-centric.

  Remove fdtbus_bs_tag definition, which is now obsolete. The remainder of
  this file is also slated for future demolition.

  Return the correct IEEE 1275 code for "nextprop".

  Use the common Open Firmware PCI interrupt routing code instead of the
  duplicate version in dev/fdt.

  Configure interrupt sense based on device tree information.

  Simplify the ofw_bus_lookup_imap() API slightly: make it allocate maskbuf
  internally instead of requiring the caller to allocate it.

git-svn-id: svn://svn.freebsd.org/base/stable/10@266020 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f