MFx86: the part of r204641
MFx86: the part of r204641

  In order to do that cleanly, lapic_setup_clock(), on both ia32 and amd64,
  now accepts as arguments the desired sources to handle, and returns the
  actual ones (LAPIC_CLOCK_NONE is forbidden because otherwise there is no
  meaning in calling such function).
  This allows to bring out into commont x86 code the handling part for
  machdep.lapic_allclocks tunable, which is retained.

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase