x86: Add DFI BT700 BayTrail board support

This patch adds support for the DFI BayTrail BT700 QSeven SoM installed
on the DFI Q7X-151 baseboard. The baseboard is equipped with the Nuvoton
NCT6102D Super IO chip providing the UART as console.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>