Pvpanic device supports bit 1 as crashloaded event, it means that
guest actually panicked and run kexec to handle error by guest side.

Handle crashloaded as a lifecyle event in libvirt.

Test case:
Guest side:
before testing, we need make sure kdump is enabled,
1, build new pvpanic driver (with commit from upstream
   e0b9a42735f2672ca2764cfbea6e55a81098d5ba
   191941692a3d1b6a9614502b279be062926b70f5)
2, insmod new kmod
3, enable crash_kexec_post_notifiers,
  # echo 1 > /sys/module/kernel/parameters/crash_kexec_post_notifiers
4, trigger kernel panic
  # echo 1 > /proc/sys/kernel/sysrq
  # echo c > /proc/sysrq-trigger

Host side:
1, build new qemu with pvpanic patches (with commit from upstream
   600d7b47e8f5085919fd1d1157f25950ea8dbc11
   7dc58deea79a343ac3adc5cadb97215086054c86)
2, build libvirt with this patch
3, handle lifecycle event and trigger guest side panic
  # virsh event stretch --event lifecycle
  event 'lifecycle' for domain stretch: Crashed Crashloaded
  events received: 1
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Nzhenwei pi <pizhenwei@bytedance.com>