mac_via: implement ADB_STATE_IDLE state if shift register in input mode

NetBSD switches directly to IDLE state without switching the shift register to
input mode. Duplicate the existing ADB_STATE_IDLE logic in input mode from when
the shift register is in output mode which allows the ADB autopoll handler to
handle the response.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-ID: <20231004083806.757242-17-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

hw/misc/mac_via.c

@@ -702,6 +702,12 @@ static void adb_via_send(MOS6522Q800VIA1State *v1s, int state, uint8_t data)
         break;
 
     case ADB_STATE_IDLE:
+        ms->b |= VIA1B_vADBInt;
+        adb_autopoll_unblock(adb_bus);
+
+        trace_via1_adb_send("IDLE", data,
+                            (ms->b & VIA1B_vADBInt) ? "+" : "-");
+
         return;
     }