KVM: PPC: Book3S PR: Handle PP0 page-protection bit in guest HPTEs

64-bit POWER processors have a three-bit field for page protection in
the hashed page table entry (HPTE).  Currently we only interpret the two
bits that were present in older versions of the architecture.  The only
defined combination that has the new bit set is 110, meaning read-only
for supervisor and no access for user mode.

This adds code to kvmppc_mmu_book3s_64_xlate() to interpret the extra
bit appropriately.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>