target/ppc: Make checkstop actually stop the system

checkstop state does not halt the system, interrupts continue to be
serviced, and other CPUs run. Make it stop the machine with
qemu_system_guest_panicked.

Reviewed-by: Glenn Miles <milesg@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
1 file changed