binder: Add binder skeletal code for Android

binder: Add binder skeletal code for Android

Create the skeletal binder interface for wpa_supplicant. The interface
hierarchy is based off the existing dbus
interface(https://w1.fi/wpa_supplicant/devel/dbus.html).

Since we use libbinder, the binder interface codebase needs to be
written in C++ and can only be compiled on Android platform for now.

The aidl files define binder RPC interfaces. The Android build system
generates the corresponding C++ interface classes which needs to be
implemented by the server process.

The clients can obtain a reference to the binder service (root object)
using:
android::String16 service_name("fi.w1.wpa_supplicant");
android::sp<android::IBinder> binder =
  android::defaultServiceManager()->getService(service_name);

Once a reference to the root object is retrieved, the clients can
obtain references to other RPC objects using that root object methods.

Signed-off-by: Roshan Pius <rpius@google.com>