idmap2: add signature policy

Handles the new signature policy for overlayable resources.

Bug: 119402606

Test: idmap2_tests target

Change-Id: I7961e04a879c40c240ed9097bb510addb8b56680
diff --git a/cmds/idmap2/libidmap2/Policies.cpp b/cmds/idmap2/libidmap2/Policies.cpp
index 0f87ef0..6649288 100644
--- a/cmds/idmap2/libidmap2/Policies.cpp
+++ b/cmds/idmap2/libidmap2/Policies.cpp
@@ -35,6 +35,7 @@
     {"product", PolicyFlags::POLICY_PRODUCT_PARTITION},
     {"system", PolicyFlags::POLICY_SYSTEM_PARTITION},
     {"vendor", PolicyFlags::POLICY_VENDOR_PARTITION},
+    {"signature", PolicyFlags::POLICY_SIGNATURE},
 };
 }  // namespace