Builds the spi-nor.img together with the sdcard.img.
Readme is extended with SPI NOR flash writing instructions
and recovery.
The spi-nor.img layout is based on the following document:
https://doc-en.rvspace.org/VisionFive2/Boot_UG/JH7110_SDK/boot_address_allocation.html
Signed-off-by: Lukasz Tekieli <tekieli.lukasz@gmail.com>
[Arnout: extend readme.txt with paragraph that either boot mode works.]
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>
