KVM: MMU: fix hashing for TDP and non-paging modes

For TDP mode, avoid creating multiple page table roots for the single
guest-to-host physical address map by fixing the inputs used for the
shadow page table hash in mmu_alloc_roots().

Signed-off-by: Eric Northup <digitaleric@google.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>