[llvm] [VPlan] Explicitly express the shift immediate for splice operation. NFC (PR #123923)

[Mel Chen via llvm-commits]

Mel-Chen wrote:

> Is the only purpose to avoid passing `Plan` to `createEVLRecipe`? 
> 
Yes.
> Could we instead make it easier to create live-in constants, maybe something like `VPlan::getOrAddInt32(int32_t Value)`? A `VPlan` object can be retrieved from the recipe itself.
>
Hmm, maybe I am a little overthinking.
Do you feel [this](https://github.com/llvm/llvm-project/pull/124093/commits/e7b6d6eb069d32127b9441b12374c157ba75ad83) is good enough, right?
Or should I add a new member function like `VPlan::getOrAddInt32(int32_t Value)` you mentioned?


https://github.com/llvm/llvm-project/pull/123923