ppc: Fix 64K pages support in full emulation

We were always advertising only 4K & 16M. Additionally the code wasn't
properly matching the page size with the PTE content, which meant we
could potentially hit an incorrect PTE if the guest used multiple sizes.

Finally, honor the CPU capabilities when decoding the size from the SLB
so we don't try to use 64K pages on 970.

This still doesn't add support for MPSS (Multiple Page Sizes per Segment)

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[clg: fixed checkpatch.pl errors
      commits 61a36c9b and 1114e712 reworked the hpte code
      doing insertion/removal in hw/ppc/spapr_hcall.c. The hunks
      modifying these areas were removed. ]
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>