Generate face HAL java-source

Bug: 194739778
Test: make and CTS cases in b/194739778
Change-Id: Iaf3cd972402017b4606fc494e4fe02acdca99767
diff --git a/biometrics/face/aidl/Android.bp b/biometrics/face/aidl/Android.bp
index 27496fb..3f53fc8 100644
--- a/biometrics/face/aidl/Android.bp
+++ b/biometrics/face/aidl/Android.bp
@@ -22,6 +22,7 @@
     backend: {
         java: {
             platform_apis: true,
+            srcs_available: true,
         },
         cpp: {
             enabled: false,