[llvm] [MCA] Parameterize variant scheduling classes by explicit variable (PR #92849)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

There was also an issue with the key lookup due to `createInstrDescImpl` calculating the actual `SchedClassID` whereas `getOrCreateInstrDesc` did not. I refactored that out so they both calculate `SchedClassID` in the same way so everything works as expected.

Thanks for the reviews!

https://github.com/llvm/llvm-project/pull/92849