[U-Boot] cfb_console and dcache on i.MX6

Hi Anatolij,

Now that the SD card driver is working properly with cache, we'd like to enable dcache on our boards, and found that this patch is still lingering without comment: http://patchwork.ozlabs.org/patch/186173/

The initial comments were here: http://patchwork.ozlabs.org/patch/186173/

If you agree with this approach, I've update the patch a bit to reflect that logo_plot() is now already static and moved the cache flush from logo_plot() to video_init().

Please advise,

Eric