Bring machine flags on par with device flag and clean up device_is_valid() accordingly.

src/pic.c

@@ -629,7 +629,7 @@ pic_reset_hard(void)
     /* The situation is as follows: There is a giant mess when it comes to these latches on real hardware,
        to the point that there's even boards with board-level latched that get used in place of the latches
        on the chipset, therefore, I'm just doing this here for the sake of simplicity. */
-    if (machine_has_bus(machine, MACHINE_BUS_PS2_LATCH)) {
+    if (machine_has_flags(machine, MACHINE_PS2_KBC)) {
         pic_kbd_latch(0x01);
         pic_mouse_latch(0x01);
     } else {