WIP: Signing TI x509 certificates using binman

Hi Simon,

Before I roll out the entire series that works for packaging K3 bootloader images, wanted to get some reviews and comments regarding the implementation of the signing etype [1] . I believe I've taken into consideration what we've discussed earlier [2].

Let me know your thoughts. The tree is also WIP, and was mainly designed for testing the signing etype on two of the devices. I will add the remaining and refine the series based on the next comments.

[1] https://github.com/nehamalcom/u-boot/commit/ea7413ed5864340bd6f01e704e8bdcc0...

[2] https://patchwork.ozlabs.org/project/uboot/patch/20230224120340.587786-1-n-f...