x86: Add defconfig for theadorable-x86-conga with PCIe x4 blobs

This defconfig uses the PCIe x4 binary blobs from the congatec BIOS.

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