dix/render: consolidate window format matching code.

This code existed in 3 different forms, perhaps it should be
consolidated.

Reviewed-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

render/picture.c

@@ -50,6 +50,14 @@ RESTYPE PictFormatType;
 RESTYPE GlyphSetType;
 int PictureCmapPolicy = PictureCmapPolicyDefault;
 
+PictFormatPtr
+PictureWindowFormat(WindowPtr pWindow)
+{
+    ScreenPtr pScreen = pWindow->drawable.pScreen;
+    return PictureMatchVisual(pScreen, pWindow->drawable.depth,
+                              WindowGetVisual(pWindow));
+}
+
 Bool
 PictureDestroyWindow(WindowPtr pWindow)
 {