Enable ARCH=um - UM Linux compiling tests - for Android Common Kernels

[helen-fornazier]

Reference: https://lore.kernel.org/kernelci/CAHRSSEwe1z7pajTmLNJRHbBv1Ghnz-siAyw4CU5kraN3_hLqpg@mail.gmail.com/T/#t

It was requested to add UML compiling tests ARCH=um SUBARCH=x86_64 to kernelci for Android Common Kernels

Add them into the new system and check the best way to report errors from it

[pawiecz]

Here's a list of steps to enable setting env variables for the builds in the new system:

1. Start by making them available to _build* functions in the kernel build abstraction package (either like here or maybe in a more generic way?)
2. Once it ^ accepts parameters, adjust kbuild job template to pass these parameters (as KBUILD_PARAMS) to executed job
3. When ^ job template is adjusted, set env vars in your new kbuild job definition; see example gcc-10-arm64 definition and its neighbors

[musamaanjum]

@helen-fornazier All the Android builds and baseline tests on arm/arm64 have been enabled. Is there anything else remaining for this issue? The PR, #528 seems outdated.