Add stubs so that portduino can build with wifi. cc @mc-hamster

src/nrf52/wifi-stubs.cpp

@@ -0,0 +1,16 @@
+#include "meshwifi/meshhttp.h"
+#include "meshwifi/meshwifi.h"
+
+void initWifi() {}
+
+void deinitWifi() {}
+
+bool isWifiAvailable()
+{
+    return false;
+}
+
+void handleWebResponse() {}
+
+/// Perform idle loop processing required by the wifi layer
+void loopWifi() {}