mmu-hash*: Add hash pte load/store helpers

mmu-hash*: Add hash pte load/store helpers

On real hardware the ppc hash page table is stored in memory; accordingly
our mmu emulation code can read a hash page table in guest memory.  But,
when paravirtualized under PAPR, the real hash page table is in host
memory, accessible to the guest only via hypercalls.  We model this by
also allowing the MMU emulation code to access a specially allocated hash
page table outside the guest's memory image. At present these two options
are implemented with some ugly conditionals at each access point in the mmu
emulation code.  In the implementation of the PAPR hypercalls, we assume
the external hash table.

This patch cleans things up by adding helpers to load and store from the
hash table for both 32-bit and 64-bit hash mmus.  The 64-bit versions
handle both the in-guest-memory and outside guest memory cases.  The 32-bit
versions only handle the in-guest-memory case since no 32-bit systems can
have an external hash table at present.

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