boot-deploy-functions: certificate exploit for omap kindle devices

OMAP HS based Kindles rely on a certificate verification exploit to chainload into a patched copy of u-boot to load unsigned images. This MR adds support for prepending the exploit header to boot.img.

tate and soho in pmaports need to be updated to use this. The other 'bowser platform' Kindles (otter2, jem) will also need this if a port gets made.

Follow up to https://gitlab.com/postmarketOS/pmaports/-/merge_requests/5473, closes #35.

cc @longnoserob @Newbyte