Currently only second stage booting from the vendor U-Boot is tested. I
don't want to flash barebox into NAND yet because UART-booting for
recovery doesn't work for me.

Working so far are:

 - UART
 - networking
 - nand flash

Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>