HAL_Empty: implement uart_info()

libraries/AP_HAL_Empty/UARTDriver.cpp

@@ -1,5 +1,6 @@
 
 #include "UARTDriver.h"
+#include <AP_Common/ExpandingString.h>
 
 Empty::UARTDriver::UARTDriver() {}
 
@@ -28,3 +29,8 @@ size_t Empty::UARTDriver::write(const uint8_t *buffer, size_t size)
     }
     return n;
 }
+
+void Empty::UARTDriver::uart_info(ExpandingString &str)
+{
+    str.printf("EMPTY\n");
+}

libraries/AP_HAL_Empty/UARTDriver.h

@@ -23,4 +23,7 @@ public:
     /* Empty implementations of Print virtual methods */
     size_t write(uint8_t c) override;
     size_t write(const uint8_t *buffer, size_t size) override;
+
+    // request information on uart I/O for one uart
+    void uart_info(ExpandingString &str) override;
 };