Replying to myself 
I could reset the SPI and get the keyboard back during boot with a simple :
flash_erase /dev/mtd0 0 0
That cleared the SPI that aparenty doesn’t contain anything necessary.
Afterwards, from within-boot :
saveenv
…wrote the default environment back to the SPI flash and allowed me to get rid of the annoying “***Warning - bad CRC” messages at boot.
(I hate seing error messages when there is no true error )