ppc/pnv: Introduce PnvPsiClass::compat

ppc/pnv: Introduce PnvPsiClass::compat

The Processor Service Interface (PSI) model has a chip_type class level
attribute, which is used to generate the content of the "compatible" DT
property according to the CPU type.

Since the PSI model already has specialized classes for each supported
CPU type, it seems cleaner to achieve this with QOM. Provide the content
of the "compatible" property with a new class level attribute.

Signed-off-by: Greg Kurz <[email protected]>
Message-Id: <157623837974.360005.14706607446188964477[email protected]>
Reviewed-by: Cédric Le Goater <[email protected]>
Signed-off-by: David Gibson <[email protected]>