Separate system_ext_property_contexts out of system sepolicy.

Bug: 137712473
Test: boot crosshatch
Change-Id: I27db30edfd9948675793fdfec19081288f8017eb
diff --git a/Android.bp b/Android.bp
index 170e7ca..e8bb270 100644
--- a/Android.bp
+++ b/Android.bp
@@ -256,6 +256,13 @@
 }
 
 property_contexts {
+    name: "system_ext_property_contexts",
+    srcs: [":property_contexts_files"],
+    system_ext_specific: true,
+    recovery_available: true,
+}
+
+property_contexts {
     name: "product_property_contexts",
     srcs: [":property_contexts_files"],
     product_specific: true,