wipe env on bootloader upgraded

[Shpinkso]

Every so often we release a new bootloader to include new feature. Often if an advanced user has been changing the uEnv this is left behind and causes boot problems. The safest thing to do is to reset this uEnv whenever the bootloader is upgraded.

Acceptance criteria:

• When programming a u-boot image into NOR with any tool (flashcp, dediprog, etc) the uEnv should get reset
• The bootloader should not print out warnings about CRC failures in uEnv on boot after programming
• Community team are informed of changes made and know how this would affect their documentation after the next release