MFC r258247, r258250, r258257

  Remove a pointless #ifdef AIM. This is just PPC64 specific, including
  64-bit Book-E.

  Make single precision floating point arithmetic actually work

  Split the function of the PCB_FPU flags into two: PCB_FPU now indicates that
  the actual FPU is enabled, while PCB_FPREGS indicates that the FPU state
  structure in the PCB is valid.
MFC r258259, r258798, r259010

  Unify handling of illegal instruction faults between AIM and Book-E.

  Make uart_cpu_powerpc work on both FDT and OFW systems.

  Fix debug printfs in FPU_EMU to compile on powerpc64 and enable it for
  powerpc64.