Add IKeystoreService interface to keystore_service

IKeystoreService is a VINTF stability interface, and keystore2 is now
using this interface correctly from Rust.

Test: m && adb shell start keystore2
Bug: 179907868
Change-Id: I3b583df2fac7e6bca7c1875efb7650f9ea0a548c
diff --git a/private/service_contexts b/private/service_contexts
index 1965d65..20a5f22 100644
--- a/private/service_contexts
+++ b/private/service_contexts
@@ -19,6 +19,7 @@
 android.hardware.vibrator.IVibratorManager/default                   u:object_r:hal_vibrator_service:s0
 android.hardware.weaver.IWeaver/default                              u:object_r:hal_weaver_service:s0
 android.frameworks.stats.IStats/default                              u:object_r:fwk_stats_service:s0
+android.system.keystore2.IKeystoreService/default                    u:object_r:keystore_service:s0
 
 accessibility                             u:object_r:accessibility_service:s0
 account                                   u:object_r:account_service:s0