target-ppc: Add new TLB invalidate by HPTE call for hash64 MMUs

When HPTEs are removed or modified by hypercalls on spapr, we need to
invalidate the relevant pages in the qemu TLB.

Currently we do that by doing some complicated calculations to work out the
right encoding for the tlbie instruction, then passing that to
ppc_tlb_invalidate_one()... which totally ignores the argument and flushes
the whole tlb.

Avoid that by adding a new flush-by-hpte helper in mmu-hash64.c.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Alexander Graf <agraf@suse.de>
