powerpc/powernv: Introduce new PHB type for opencapi links

The NPU was already abstracted by opal as a virtual PHB for nvlink,
but it helps to be able to differentiate between a nvlink or opencapi
PHB, as it's not completely transparent to linux. In particular, PE
assignment differs and we'll also need the information in later
patches.

So rename existing PNV_PHB_NPU type to PNV_PHB_NPU_NVLINK and add a
new type PNV_PHB_NPU_OCAPI.

Signed-off-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>