Gamepad (Haiku): add support

src/detection/gamepad/gamepad_haiku.cpp

@@ -0,0 +1,21 @@
+extern "C" {
+#include "gamepad.h"
+}
+#include <Joystick.h>
+
+const char* ffDetectGamepad(FFlist* devices /* List of FFGamepadDevice */)
+{
+    BJoystick js;
+    for (int32 i = 0, n = js.CountDevices(); i < n; ++i)
+    {
+        char name[B_OS_NAME_LENGTH];
+        if (js.GetDeviceName(i, name) == B_OK)
+        {
+            FFGamepadDevice* device = (FFGamepadDevice*) ffListAdd(devices);
+            ffStrbufInit(&device->serial);
+            ffStrbufInitS(&device->name, name);
+            device->battery = 0;
+        }
+    }
+    return NULL;
+}