ppc/pnv: Introduce PnvChipClass::xscom_pcba() method

ppc/pnv: Introduce PnvChipClass::xscom_pcba() method

The XSCOM bus is implemented with a QOM interface, which is mostly
generic from a CPU type standpoint, except for the computation of
addresses on the Pervasive Connect Bus (PCB) network. This is handled
by the pnv_xscom_pcba() function with a switch statement based on
the chip_type class level attribute of the CPU chip.

This can be achieved using QOM. Also the address argument is masked with
PNV_XSCOM_SIZE - 1, which is for POWER8 only. Addresses may have different
sizes with other CPU types. Have each CPU chip type handle the appropriate
computation with a QOM xscom_pcba() method.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <157623843543.360005.13996472463887521794.stgit@bahia.lan>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>