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>