KVM: PPC: Separate loadstore emulation from priv emulation

Today the instruction emulator can get called via 2 separate code paths. It
can either be called by MMIO emulation detection code or by privileged
instruction traps.

This is bad, as both code paths prepare the environment differently. For MMIO
emulation we already know the virtual address we faulted on, so instructions
there don't have to actually fetch that information.

Split out the two separate use cases into separate files.

Signed-off-by: Alexander Graf <agraf@suse.de>