MFC r258359, r258742, r258845, r259936, r259640

  Apply access flags for managed and unmanaged pages properly on ARMv6/v7

  Set the PGA_WRITEABLE flag when the protections indicate write access, not
  just when the current access is a write.

  Enable missing Access Flag for secondary cores on ARMv6/v7

  Add identification and necessary type checks for Krait CPU cores.