KVM: PPC: Book3S HV: Access host lppaca and shadow slb in BE

Some data structures are always stored in big endian. Among those are the LPPACA
fields as well as the shadow slb. These structures might be shared with a
hypervisor.

So whenever we access those fields, make sure we do so in big endian byte order.

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