TalkBack does not announce properly the buttons of the PIN lock.

The KeyBoardView shown by the lock screen is not marked as clickable even
though it handles clicks. TalkBack uses the clickability as a clue of what
to speak.

bug:5713102

Change-Id: I0733e30619e6045ce3f78e1499db65f4dc5bc388

core/res/res/layout-sw600dp/keyguard_screen_password_landscape.xml

@@ -134,6 +134,7 @@
                 android:layout_marginTop="5dip"
                 android:keyBackground="@drawable/btn_keyboard_key_ics"
                 android:visibility="gone"
+                android:clickable="true"
             />
 
             <!-- Emergency call button. Generally not used on tablet devices. -->

core/res/res/layout-sw600dp/keyguard_screen_password_portrait.xml

@@ -133,6 +133,7 @@
             android:background="#40000000"
             android:keyBackground="@drawable/btn_keyboard_key_ics"
             android:layout_marginBottom="80dip"
+            android:clickable="true"
         />
 
         <!-- emergency call button -->

core/res/res/layout/keyguard_screen_password_landscape.xml

@@ -193,6 +193,7 @@
         android:keyBackground="@*android:drawable/btn_keyboard_key_ics"
         android:visibility="gone"
         android:layout_rowSpan="7"
+        android:clickable="true"
     />
 
     <!-- Music transport control -->

core/res/res/layout/keyguard_screen_password_portrait.xml

@@ -157,6 +157,7 @@
         android:background="#40000000"
         android:keyBackground="@*android:drawable/btn_keyboard_key_ics"
         android:visibility="gone"
+        android:clickable="true"
     />
 
     <TextView