KVM: PPC: Book3S HV: Make HPT-specific hypercalls return error in radix mode

If the guest is in radix mode, then it doesn't have a hashed page
table (HPT), so all of the hypercalls that manipulate the HPT can't
work and should return an error.  This adds checks to make them
return H_FUNCTION ("function not supported").

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>