KVM: PPC: e500: Implement TLB1-in-TLB0 mapping

When a host mapping fault happens in a guest TLB1 entry today, we
map the translated guest entry into the host's TLB1.

This isn't particularly clever when the guest is mapped by normal 4k
pages, since these would be a lot better to put into TLB0 instead.

This patch adds the required logic to map 4k TLB1 shadow maps into
the host's TLB0.

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