Commit 31168f033e37 is correct that pud_index() & __pud_offset() are the same
when pud_index() is actually provided, however it does not take into account[...]
the __PAGETABLE_PUD_FOLDED case. Provide kvm_pud_index so that MIPS KVM
compiles.
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>