ppc/xics: fix ICP reset path

ppc/xics: fix ICP reset path

Recent cleanup in commit a028dd423ee6 dropped the ICPStateClass::reset
handler. It is now up to child ICP classes to call the DeviceClass::reset
handler of the parent class, thanks to device_class_set_parent_reset().
This is a better object programming pattern, but unfortunately it causes
QEMU to crash during CPU hotplug:

(qemu) device_add host-spapr-cpu-core,id=core1,core-id=1
Segmentation fault (core dumped)

When the hotplug path tries to reset the ICP device, we end up calling:

static void icp_kvm_reset(DeviceState *dev)
{
    ICPStateClass *icpc = ICP_GET_CLASS(dev);

    icpc->parent_reset(dev);

but icpc->parent_reset is NULL... This happens because icp_kvm_class_init()
calls:

    device_class_set_parent_reset(dc, icp_kvm_reset,
                                  &icpc->parent_reset);

but dc->reset, ie, DeviceClass::reset for the TYPE_ICP type, is
itself NULL.

This patch hence sets DeviceClass::reset for the TYPE_ICP type to
point to icp_reset(). It then registers a reset handler that calls
DeviceClass::reset. If the ICP subtype has configured its own reset
handler with device_class_set_parent_reset(), this ensures it will
be called first and it can then call ICPStateClass::parent_reset
safely. This fixes the reset path for the TYPE_KVM_ICP type, which
is the only subtype that defines its own reset function.

Reported-by: Satheesh Rajendran <sathnaga@linux.vnet.ibm.com>
Suggested-by: David Gibson <david@gibson.dropbear.id.au>
Fixes: a028dd423ee6dfd091a8c63028240832bf10f671
Signed-off-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>