i8259: Convert PICCommonState to use QOM realizefn

Instead of having the parent provide PICCommonClass::init,
let the children override DeviceClass::realize themselves.
This pushes the responsibility of saving and calling the parent's
realizefn to the children.

Signed-off-by: Andreas Färber <afaerber@suse.de>

include/hw/isa/i8259_internal.h

@@ -42,7 +42,7 @@ typedef struct PICCommonState PICCommonState;
 typedef struct PICCommonClass
 {
     ISADeviceClass parent_class;
-    void (*init)(PICCommonState *s);
+
     void (*pre_save)(PICCommonState *s);
     void (*post_load)(PICCommonState *s);
 } PICCommonClass;