board: sama5d2_xplained: Enable an early debug UART

Enable an early debug UART to debug problems when an ICE or other
debug mechanism is not available.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Andreas Bießmann <andreas.devel@googlemail.com>
4 files changed