ECBM SystemProperty cleanup

- Add getEmergencyCallbackMode() method to get the boolean
value for ECBM callback mode from the phone, in the
PhoneInterfaceManager.java

- Replace the 'get' of PROPERTY_INECM_MODE system property
in the packages/services/Telephony

Test: Manual
Bug: 30361624
Change-Id: I23c3fa0c985efb28bf37f2d7ee1c85b732cc7b0d
diff --git a/src/com/android/phone/PhoneInterfaceManager.java b/src/com/android/phone/PhoneInterfaceManager.java
index 89e484a..2165a48 100644
--- a/src/com/android/phone/PhoneInterfaceManager.java
+++ b/src/com/android/phone/PhoneInterfaceManager.java
@@ -3611,4 +3611,18 @@
             phone.setSimPowerState(powerUp);
         }
     }
+
+    /**
+     * Check if phone is in emergency callback mode
+     * @return true if phone is in emergency callback mode
+     * @param subId sub id
+     */
+    public boolean getEmergencyCallbackMode(int subId) {
+        final Phone phone = getPhone(subId);
+        if (phone != null) {
+            return phone.isInEcm();
+        } else {
+            return false;
+        }
+    }
 }