Feature flag for emergency registration CB feature

Define feature flag for emergency registration notification feature

Bug: 312101946
Test: system build
Change-Id: Id70cf14453378cd01542377ca24cf813cad1fb86
diff --git a/flags/ims.aconfig b/flags/ims.aconfig
index 4638194..92d003d 100644
--- a/flags/ims.aconfig
+++ b/flags/ims.aconfig
@@ -41,3 +41,10 @@
     description: "This flag terminates active video call instead holding when accepting 2nd incoming video call as audio only"
     bug:"309548300"
 }
+
+flag {
+    name: "emergency_registration_state"
+    namespace: "telephony"
+    description: "This flag is created to notify emergency registration state changed."
+    bug:"312101946"
+}