uboot-imx

x86: Init the debug UART if enabled

If the debug UART is enabled, get it ready for use at the earliest possible
opportunity. This is not actually very early, but until we have a stack it
is difficult to make it work.

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