powerpc/fsl-booke: Cleanup init/exception setup to be runtime

We currently have a few variants of fsl-booke processors (e500v1, e500v2,
e500mc, and e200).  They all have minor differences that we had previously
been handling via ifdefs.

To move towards having this support the following changes have been made:

* PID1, PID2 only exist on e500v1 & e500v2 and should not be accessed on
  e500mc or e200.  We use MMUCFG[NPIDS] to determine which case we are
  since we only touch PID1/2 in extremely early init code.

* Not all IVORs exist on all the processors so introduce cpu_setup
  functions for each variant to setup the proper IVORs that are either
  unique or exist but have some variations between the processors

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>