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.
The NAND might have more bit flips than can be recovered. The way
to deal with it is to write multiple copies on multiple pages. The
probability of all pages failing depends on the specific NAND flash
used and was not calculated so far. The RBL is capable of trying to
load several copies and we should be more safe now.
This requires a new partioning inside the U-Boot or other bootloader.