hw/arm_gic.c: Define .class_size in arm_gic_info TypeInfo

Add the missing .class_size definition to the arm_gic_info TypeInfo.
This fixes the memory corruption and possible segfault that otherwise
results when the class struct is allocated at too small a size and
the class init function writes off the end of it.
Reported-by: NAdam Lackorzynski <adam@os.inf.tu-dresden.de>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/arm_gic.c

@@ -703,6 +703,7 @@ static TypeInfo arm_gic_info = {
     .parent = TYPE_ARM_GIC_COMMON,
     .instance_size = sizeof(gic_state),
     .class_init = arm_gic_class_init,
+    .class_size = sizeof(ARMGICClass),
 };
 
 static void arm_gic_register_types(void)