xics: Eliminate reset hook

xics: Eliminate reset hook

Currently TYPE_XICS_BASE and TYPE_XICS_SIMPLE have their own reset methods,
using the standard technique for having the subtype call the supertype's
methods before doing its own thing.

But TYPE_XICS_SIMPLE is the only subtype of TYPE_XICS_BASE ever
instantiated, so there's no point having the split here.  Merge them
together into just an ics_reset() function.

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