Parameterize a spacing dimen in dialpad

I intend to override these values inside Telephony.

Bug: 17380050
Change-Id: I27485585c5fda2edbf0b1444b85aba0379c9cd28
diff --git a/res/layout/dialpad_view.xml b/res/layout/dialpad_view.xml
index 9340667..a6ff7aa 100644
--- a/res/layout/dialpad_view.xml
+++ b/res/layout/dialpad_view.xml
@@ -86,7 +86,7 @@
 
     <Space
         android:layout_width="match_parent"
-        android:layout_height="14dp" />
+        android:layout_height="@dimen/dialpad_space_above_keys" />
 
     <include layout="@layout/dialpad" />