Make UsbService optional

Tweaked the services Android.mk to build dependencies
when building with mm[m].

Change-Id: I6dad511c652bcacc085f27ede5f8f22a6982c6bd
diff --git a/services/usb/Android.mk b/services/usb/Android.mk
new file mode 100644
index 0000000..feabf0a
--- /dev/null
+++ b/services/usb/Android.mk
@@ -0,0 +1,12 @@
+LOCAL_PATH := $(call my-dir)
+
+include $(CLEAR_VARS)
+
+LOCAL_MODULE := services.usb
+
+LOCAL_SRC_FILES += \
+      $(call all-java-files-under,java)
+
+LOCAL_JAVA_LIBRARIES := services.core
+
+include $(BUILD_STATIC_JAVA_LIBRARY)