Add compatibility wrapper

This implements the Keymint 1 spec by wrapping the legacy Keymaster
implementation.

Test: atest keystore2_km_compat_test
Test: atest keystore2_certificate_test
Test: Manually verify that keystore2 can find a legacy implementation.
Change-Id: Ia56c25eed0f97a7e6194954a655ceb62259b3273
diff --git a/keystore2/aidl/Android.bp b/keystore2/aidl/Android.bp
index 3051173..0d05dfe 100644
--- a/keystore2/aidl/Android.bp
+++ b/keystore2/aidl/Android.bp
@@ -58,3 +58,21 @@
         },
     },
 }
+
+aidl_interface {
+    name: "android.security.compat",
+    srcs: [ "android/security/compat/*.aidl" ],
+    imports: [ "android.hardware.security.keymint" ],
+    unstable: true,
+    backend: {
+        java: {
+            sdk_version: "module_current",
+        },
+        rust: {
+            enabled: true,
+        },
+        ndk: {
+            enabled: true,
+        }
+    },
+}