powerpc/mm/radix: Update machine call back to support new HCALL.

This update the machine dep callback such that we can use the same
callback to register process table. The interface is updated such that
we can easily call H_REGISTER_PROC_TBL hcall. The HCALL itself is
introduced in a later patch.

No functionality change introduced by this patch.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>