mmu-hash*: Don't use full ppc_hash{32, 64}_translate() path for get_phys_page_debug()

Currently the hash mmu versionsof get_phys_page_debug() use the same
ppc64_hash64_translate() function to do the translation logic as the normal
mm fault handler code.

That sounds like a good idea, but has some complications. The debug path
doesn't need, or even want some parts of the full translation path, like
permissions checking.  Furthermore, the pte flags update included in the
normal path means that the debug call is not quite side effect free.

This patch, therefore, reimplements get_phys_page_debug as the minimal
required subset of the full translation path.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>`z
Signed-off-by: Alexander Graf <agraf@suse.de>
