KVM: ppc: Rename "struct tlbe" to "struct kvmppc_44x_tlbe"

This will ease ports to other cores.

Also remove unused "struct kvm_tlb" while we're at it.

Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>