gpu: call CreateScreenResources for GPU screens

I didn't think we needed this before, but after doing some more
work with reverse optimus it seems like it should be called.

Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

dix/main.c

@@ -211,6 +211,9 @@ main(int argc, char *argv[], char *envp[])
             ScreenPtr pScreen = screenInfo.gpuscreens[i];
             if (!CreateScratchPixmapsForScreen(pScreen))
                 FatalError("failed to create scratch pixmaps");
+            if (pScreen->CreateScreenResources &&
+                !(*pScreen->CreateScreenResources) (pScreen))
+                FatalError("failed to create screen resources");
         }
 
         for (i = 0; i < screenInfo.numScreens; i++) {