PowerPC config options

[Josh Boyer]

Couple of PowerPC related config things we might want to change.

1) CONFIG_TUNE_CELL.  Right now, this is set to Y on config-powerpc64.
That's fine only because it doesn't do anything until GCC 4.3 shows
up.  GCC 4.3 will hit rawhide soon, and we might want to turn this off
before then or the kernel will likely run slower on non-Cell CPU based
machines.

2) Why are we still building a separate powerpc32-smp kernel?  SMP
kernel's work on UP machines, even for PowerPC IIRC.

josh