Switch `llvm/CodeGen/MachineValueType.h` to the generated one

[chapuni]

Summary

Prune SupportTests/MVTTest since it is no longer needed.

See also, "[RFC] Let MVT generated and restore MVT into llvm/CodeGen"
https://discourse.llvm.org/t/rfc-let-mvt-generated-and-restore-mvt-into-llvm-codegen/69547

Depends on D148769

[chapuni]

• Update desc

[chapuni]

• fix a typo in modmap

[chapuni]

These series can close my RFC. Feel free to add other reviewers/subscribers.

"[RFC] Let MVT generated and restore MVT into llvm/CodeGen"
https://discourse.llvm.org/t/rfc-let-mvt-generated-and-restore-mvt-into-llvm-codegen/69547

[chapuni]

• Update CMake deps

[chapuni]

• Rebase

[chapuni]

I have found the case aarch64svcount is incompatible. Will fix.

[chapuni]

Fixed temporarily in rGd091a19e58a2.

[thakis]

This adds a dependency cycle:

//llvm/utils/TableGen:llvm-tblgen ->
//llvm/utils/TableGen/GlobalISel:GlobalISel ->
//llvm/include/llvm/CodeGen:GenVT ->
//llvm/utils/TableGen:llvm-tblgen

[thakis]

Oh I see, that's what D146352 is for.

That's a lot of machinery. Is there any benefit to these changes too to justify that?