[llvm] [MIR] Serialize virtual register flags (PR #110228)

[Christudasan Devadasan via llvm-commits]

cdevadas wrote:

Missing new test for this serialized field.
Add a valid test here llvm/test/CodeGen/MIR/AMDGPU/machine-function-info-no-ir.mir
Also, capture all invalid cases in a negative test.

https://github.com/llvm/llvm-project/pull/110228