Change in coreboot[master]: Add mediatek mt8192 dram vendor code

[Nico Huber (Code Review)]

Attention is currently required from: Hung-Te Lin, Xi Chen, Martin Roth, Paul Menzel, Yu-Ping Wu.
Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/50294 )

Change subject: Add mediatek mt8192 dram vendor code
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Patch Set 5:

(2 comments)

Commit Message:

https://review.coreboot.org/c/coreboot/+/50294/comment/b39ba838_c210eed5 
PS5, Line 11:
> xixi's comments and the way he merged patches may lead to confusion. […]

That the code is developed/maintained somewhere else is a perfect argument
to put it into vendorcode/.

However, in case Mediatek maintains a public Git repository, we could also
integrated that as a submodule. I assume they don't do that?

Patchset:

PS5:
> No, you have to make it clear "here's a drop from MTK's official release". […]

As this is not a clean move (it seems to add a newer version), I think two
patches would be cleaner. One that adds the current Mediatek-maintained
version. It can mention the version etc. and that this is maintained some-
where else, in the commit message. And a second that updates soc/ to use
the new vendorcode.