[U-Boot] mx6sabresd: Use VESA 1024x768 timings

[Soeren Moch]

> VESA 1024x768 results in much more accurate timings.
>
> Based on the patch from Soeren Moech for the tbs2910 board.

Soeren Moch

;-)

>
> Signed-off-by: Fabio Estevam <fabio.estevam at nxp.com>

Regards,
Soeren