EDIT: I see my suggested correct URL is for R32.3.1, JetPack4.3. You would actually want the same thing, but based on the older JetPack3.3.
Your URL will not work as is. You clicked on the “url” tag, which needs a web server to work with, but what you have is a file. If you hover your mouse over the quote icon in the upper right of your existing post, then other icons will show up. The paper clip icon is for attaching files. The pencil icon is to edit your existing post.
If you probably want to you could edit with the pencil icon, and remove the URL, or change the URL. Then save the edit. If and only if you really want to attach a file (and for an HTML web page you do not want to attach the file), then you would then hover the mouse over the quote icon and click on the paper clip icon. With this you can attach a file (in your case though you are naming an HTML file on your local computer, and attaching this would not make sense).
On the other hand, this file is available on the NVIDIA web site, and you could refer to that instead of your local copy on your PC. If you go here and select product TX2, then you can see TX2 documents (redirect does not work, so you will probably need to go there, log in, and then go there again):
The URL of the document you are actually interested in posting the URL for, as an online document and not as an attached file, is (if you were using JetPack4.3):
I cannot answer what you are actually missing, but no doubt your configuration does not include everything the default U-Boot includes (and I do not know the default U-Boot configuration, so this is why I can’t answer). Normally you would match the existing configuration, and then add or edit whatever you want. Editing source code could mean you just want the original configuration and have no need to change the config…you’d be working directly on source code edits rather than configuration edits.
One possibility is the configurations needed for PCIe were lost. Another possibility is that i2c configuration was lost. Either of those would cause a PCIe i2c device to go missing. No driver, no detect. In some cases it is also possible that a device tree might not correctly name the path to the PCIe or i2c, and in that case U-Boot would not be able to find the device even if the U-Boot binary itself has the drivers.
Someone else may be able to tell you how to match the U-Boot configuration to the stock U-Boot binary. Once this is a known match, if things still fail, then you can search for other possibilities, e.g., the device tree.