Move IMS configuration constants from packages/apps/Settings to common location

Constants for Enhanced 4G LTE Mode needed in packages/apps/Settings as well as
in other shared code (e.g. GSMPhone, CDMAPhone). Moved to shared (common)
location.

Change-Id: I0a718218f2e75754346e1caafaa4250000706ad6
diff --git a/src/java/com/android/ims/ImsManager.java b/src/java/com/android/ims/ImsManager.java
index b33517f..0061d3d 100644
--- a/src/java/com/android/ims/ImsManager.java
+++ b/src/java/com/android/ims/ImsManager.java
@@ -48,6 +48,12 @@
  * @hide
  */
 public class ImsManager {
+    /*
+     * Shared preference constants storing the "Enhanced 4G LTE Mode" configuration
+     */
+    public static final String IMS_SHARED_PREFERENCES = "IMS_PREFERENCES";
+    public static final String KEY_IMS_ON = "IMS";
+
     /**
      * For accessing the IMS related service.
      * Internal use only.