MIPS: smp-cps: Disable coherence setup for unsupported ISA

We don't know how to do coherence setup on ISA before MIPS
Release 1.

As CPS support only servers simulation purpose on those cores,
and simulators are always coherent, just disable initialization
code and provide user a warning in case coherence is not setup
properly.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>