Fix QS tiles not rippling

It was due to complicated background changes added for the gutter,
add a transparent background for QS + header to give the ripples
a location to draw on.

Test: visual
Change-Id: I59c2d0b1fb543852e54980577b1ce7307b6e4de8
Fixes: 38330186

packages/SystemUI/res/layout/qs_panel.xml

@@ -35,6 +35,7 @@
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:elevation="4dp"
+        android:background="#00000000"
         android:layout_marginBottom="48dp" />
 
     <include layout="@layout/quick_status_bar_expanded_header" />

packages/SystemUI/res/layout/quick_status_bar_expanded_header.xml

@@ -24,6 +24,7 @@
     android:layout_height="@dimen/status_bar_header_height"
     android:layout_gravity="@integer/notification_panel_layout_gravity"
     android:baselineAligned="false"
+    android:background="#00000000"
     android:elevation="4dp"
     android:clickable="false"
     android:clipChildren="false"