AnalogOut: Add explicit pinmap support

drivers/AnalogOut.h

@@ -66,6 +66,15 @@ public:
         analogout_init(&_dac, pin);
     }
 
+    /** Create an AnalogOut connected to the specified pin
+     *
+     * @param pinmap reference to strucure which holds static pinmap.
+     */
+    AnalogOut(const PinMap &pinmap)
+    {
+        analogout_init_direct(&_dac, &pinmap);
+    }
+
     /** Set the output voltage, specified as a percentage (float)
      *
      *  @param value A floating-point value representing the output voltage,