Merge tag 'spi-nor/for-6.8' into mtd/next

SPI NOR comes with die erase support for multi die flashes, with new
octal protocols (1-1-8 and 1-8-8) parsed from SFDP and with an updated
documentation about what the contributors shall consider when proposing
flash additions or updates. Michael Walle stepped out from the reviewer
role to maintainer.