Add a Global setting for disabling OEM unlocking setting

+ By default, OEM unlocking setting is enabled.
+ Add a check to prevent oem unlock being flipped if the setting isn't
  enabled.

Bug: 28163088
Change-Id: I087d8d5a1d99a611a8f66ff71a92ec9ea1da4e9f
diff --git a/core/java/android/provider/Settings.java b/core/java/android/provider/Settings.java
index d80d4be..8dc14c0 100755
--- a/core/java/android/provider/Settings.java
+++ b/core/java/android/provider/Settings.java
@@ -8759,6 +8759,15 @@
          * @hide
          */
         public static final String ENABLE_CELLULAR_ON_BOOT = "enable_cellular_on_boot";
+
+        /**
+         * Whether toggling OEM unlock is disallowed. If disallowed, it is not possible to enable or
+         * disable OEM unlock.
+         * <p>
+         * Type: int (0: allow OEM unlock setting. 1: disallow OEM unlock)
+         * @hide
+         */
+        public static final String OEM_UNLOCK_DISALLOWED = "oem_unlock_disallowed";
     }
 
     /**