[llvm] [RISCV][NFC] Allow SchedVar to be a def inside our scheduler model files. (PR #82634)

[Craig Topper via llvm-commits]

topperc wrote:

Why does `VLDSX0Pred` need to be inside the SiFive7Base class? There's nothing that changes based on which model uses it. It could just be a top level record.

https://github.com/llvm/llvm-project/pull/82634