Implemetion of BusDevice and PciDevice trait for pvpanic device.
Pvpanic device can be implemented as an ISA device or as a
PCI device, we choose PCI device for now.
Signed-off-by: Yi Wang <foxywang@tencent.com>
Introduce emulation of pvpanic device to allow cloud hypervisor to get
the notify from guest's pvpanic driver when guest kernel crash.
Signed-off-by: Yi Wang <foxywang@tencent.com>