x86: conga-qeval20-qa3: Add support for internal UART

This patch adds support to enable and use the internal BayTrail UART
instead of the one integrated in the Super IO Winbond chip. For this,
a 2nd defconfig file is added.

This is useful for tests done for the congatec SoM used on baseboards
without such a Super IO chip.

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