Have you tried to upgrade the board firmware to the last version before proceeding with the image building?
I am going to build yocto and the bootloader.
yocto will be in the SD and the bootloader will be in the flash rom.
As I know, I have to build everything including the flash image and platform data.
Would you please let me know what firmware need to be upgrade ? Do you mean flash image + platform data ?
In order to upgrade to the latest firmware, you need to run the Arduino IDE and go to Help tab, then click on Firmware Update.
Do you still need help with your BSP build?
Can you provide the message that is displayed when your build fails?