Android: don't compile powermgmt-sim.c

Instead implement a bit of battery monitoring. Currently it only fetches the battery level (in %) every 30s,
but it could do more like battery status, charger connected, voltage...
Theoretically, we could also exit/quit after some time of inactivity too
(perhaps not a bad idea since Rockbox puts a slight but still non-zero CPU load even if doing nothing).

Ironically, Rockbox is now the only way to get the exact battery level (at least I haven't found anything yet) on my phone :-)

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@27974 a1c6a512-1295-4272-9138-f99709370657

firmware/target/hosted/android/system-android.c

@@ -55,5 +55,8 @@ Java_org_rockbox_RockboxService_main(JNIEnv *env, jobject this)
     env_ptr = env;
     RockboxService_instance = this;
     RockboxService_class = (*env)->GetObjectClass(env, this);
+
+
+    powermgmt_init_target();
     main();
 }