[coreboot] Refactor tianocore payload

[Patrick Rudolph]

Hi folks!

With UEFI the defactor standard it seems reasonable to improve the
tianocore payload integration.

I'm having trouble to compile "stable" and "master" is totally broken
as packages have been removed.

Instead of the current approach of maintaining patches in our tree, I'd
like to use a repo that has those patches applied and is known to be
working.

A good candiate is [1], as it's maintained, has bug-fixes and features
upstream tianocore doesn't provide, and it's known to work with
coreboot out of the box.

Similar to seabios, we should use this repo without additional in-tree
patches to build a working payload.

Please tell me what you think about the proposed solution.

[1]: https://github.com/MrChromebox/edk2