Most of the function that wrap it can be rewritten without it, except
for gfn_to_pfn_prot.  Just inline it into gfn_to_pfn_prot, and rewrite
the other function on top of gfn_to_pfn_memslot*.
Reviewed-by: Radim Krcmar <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>