Help the boot loader and perform a bus clear. U-Boot will try to
read the MAC from the EEPROM and barebox has the complex boot
state stored in it.
In the past we have seen U-boot failing to read from the EEPROM
and let's have one place to initialize it.
Starting from revision F we can toggle a GPIO to control nWP of
the NAND chip. This means that during power-on or other mode of
operation no changes can be done to the flash.
Remove the nWP before we try to write to the flash in the UART
mode. Leave it enabled for further operations.
Holger Hans Peter Freyther