spapr_pci: Eliminate class callbacks

spapr_pci: Eliminate class callbacks

The EEH operations in the spapr-vfio-pci-host-bridge no longer rely on the
special groupid field in sPAPRPHBVFIOState.  So we can simplify, removing
the class specific callbacks with direct calls based on a simple
spapr_phb_eeh_enabled() helper.  For now we implement that in terms of
a boolean in the class, but we'll continue to clean that up later.

On its own this is a rather strange way of doing things, but it's a useful
intermediate step to further cleanups.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>