enable the final slot

The debug uart is shared with slot 7, so in order to use sim slot 7 the
pin config and the uart config needs to be changed. Going back to using
the debug uart works by defining ENABLE_DBG_UART7

Change-Id: I8f3c7c60306941159c35307a5c1e38c2a2bd2fe1
diff --git a/sysmoOCTSIM/stdio_start.c b/sysmoOCTSIM/stdio_start.c
index 8a15c88..63e125d 100644
--- a/sysmoOCTSIM/stdio_start.c
+++ b/sysmoOCTSIM/stdio_start.c
@@ -9,6 +9,7 @@
 #include "atmel_start.h"
 #include "stdio_start.h"
 
+#ifdef ENABLE_DBG_UART7
 static void UART_debug_rx_cb(const struct usart_async_rings_descriptor *const io_descr)
 {
 }
@@ -19,3 +20,4 @@
 	usart_async_rings_enable(&UART_debug);
 	stdio_io_init(&UART_debug.io);
 }
+#endif