Keep SLB in-CPU

Keep SLB in-CPU

Real 970 CPUs have the SLB not memory backed, but inside the CPU.
This breaks bridge mode for 970 for now, but at least keeps us from
overwriting physical addresses 0x0 - 0x300, rendering our interrupt
handlers useless.

I put in a stub for bridge mode operation that could be enabled
easily, but for now it's safer to leave that off I guess (970fx doesn't
have bridge mode AFAIK).

Signed-off-by: Alexander Graf <alex@csgraf.de>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6757 c046a42c-6fe2-441c-8c8c-71466251a162