x86: Add theadorable-x86-dfi-bt700 board support

This patch adds support for the BayTrail based theadorable-x86-dfi-bt700
board which uses the DFI BT700 BayTrail Qseven SoM on a custom baseboard.
The main difference to the DFI baseboard is, that it isn't equipped
with a Super IO chip and uses the internal HS SIO UART (memory mapped
PCI based) as the console UART.

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