powerpc: Simplify processor.h

Lots of stuff in processor.h was taken verbatim from the Linux kernel.
It was never synced, so most of it was removed or changed in the kernel
since it was imported.

Remove all the stuff that is unused in the current U-Boot sources;
should anybody feel the need to re-sync with the kernel, they can do it
later on.

Signed-off-by: Mario Six <mario.six@gdsys.cc>