xics: pass appropriate types to realize() handlers.

It makes more sense to pass an IPCState * to handlers of ICPStateClass
instead of a DeviceState *, if only to benefit from compile time type
checking. The same goes with ICSStateClass.

While here, we also change the declaration of ICPStateClass in xics.h
for consistency.

Signed-off-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
