x86: baytrail: Fix boot hang with a debug build

x86: baytrail: Fix boot hang with a debug build

It was observed that when -DDEBUG is used to generate a debug build,
U-Boot does not boot on MinnowMax board. A workaround is to disable
CONFIG_DEBUG_UART. The real issue is that in order to have the debug
uart to work, BayTrail SoC needs to be configured so that its internal
uart is available to be used as the debug uart.

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