[POWERPC] MPC5200: Don't make firmware fixups into common code

The Lite5200 u-boot image doesn't entirely configure the processor
correctly and so Linux needs to fixup the cpu setup in setup_arch.  Fixing
the CPU setup is good, but making it into common code is not a good idea.

New board ports should be encouraged not to take the lead of the lite5200
and instead get their firmware to setup the CPU the right way.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Sylvain Munaut <tnt@246tnt.com>