PCPU fields for curthread, by doing the same to Book-E. This closes
some potential races switching between CPUs. As a side effect, it turns out
the AIM and Book-E swtch.S implementations were the same to within a few
registers, so move that to powerpc/powerpc.
MFC after: 3 months
at least on my Xserve, getting the decrementer and timebase on APs to tick
requires setting up a clock chip over I2C, which is not yet done.
While here, correct the 64-bit tlbie function to set the CPU to 64-bit
mode correctly.
Hardware donated by: grehan
