Disable FBC by default on 965GM

Several people have reported that they see frequent FBC related display
corruption on 965GM, so disable it for now.  Users wanting to enable it can use
the driver option "Framebuffercompression" to override the default.

src/i830_driver.c

@@ -2449,7 +2449,7 @@ I830ScreenInit(int scrnIndex, ScreenPtr pScreen, int argc, char **argv)
    }
 
    /* Enable FB compression if possible */
-   if (i830_fb_compression_supported(pI830))
+   if (i830_fb_compression_supported(pI830) && !IS_I965GM(pI830))
        pI830->fb_compression = TRUE;
    else
        pI830->fb_compression = FALSE;