feat(U-Boot): Add OTP Key Writer User Guide

[Harsha-VM]

Add a KeyWriter guide describing the procedure to program customer keys into the eFuses using U-Boot's fuse writebuff command, enabling HS-FS to HS-SE device conversion.

The guide covers:

• Background on HS-FS and HS-SE device sub-types
• The fuse_otp binary blob structure with a diagram illustrating the layout
• Step-by-step key writer example flow
• Post-programming note that eFuse changes require a full SoC power cycle to take effect

Register the new page in the AM62LX Linux TOC and U-Boot Users Guide index.

[sadik-smd]

@shiva-ti @jsuhaas22 to review

[StaticRocket]

@Harsha-VM this was opened as a draft and never marked ready for review. Is there any additional pending work for this or should it go through proper review now?

[Harsha-VM]

@Harsha-VM this was opened as a draft and never marked ready for review. Is there any additional pending work for this or should it go through proper review now?

@StaticRocket Marked it ready for review now

[StaticRocket]

What's actually the difference between Key Writer Lite and Key Writer ? The two files are almost exactly the same. This just seems to explicitly change the i2c dev to 2 instead of 1 for AM62L specifically. Seems odd.

[cshilwant]

@shiva-ti @jsuhaas22 for review

[Harsha-VM]

What's actually the difference between Key Writer Lite and Key Writer ? The two files are almost exactly the same.

@StaticRocket These are 2 different methods of secure key provisioning offered by TIFS. Keywriter Lite is used to convert the device to a HS-SE lite device(without encryption support) where Keywriter is used to convert the device to a HS-SE device(with encryption support). So, the structure layout and method of preparation differ between the both.

This just seems to explicitly change the i2c dev to 2 instead of 1 for AM62L specifically. Seems odd.

On this, 1 is the right bus, and it has been updated in the keywriter lite doc as well!

[StaticRocket]

@Harsha-VM could we add this information to the introduction paragraph? I feel like that's an important distinction to make up front. Also, there's currently mixed use of key writer and keywriter. The TI-SCI documentation has a similar problem. What did we actually call this?

[StaticRocket]

@liubiin this also feels like it's reaching into academy territory as it's more of a how-to guide