[llvm] [AArch64][CostModel] Consider the cost of const vector (PR #117539)

[Sushant Gokhale via llvm-commits]

sushgokh wrote:

@davemgreen 
> * Including the costs somehow is probably a good idea, but there are reasons why this has not been done before. We should try and come up with a consistent way of doing it, ideally.

Having something like [this](https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/AArch64/AArch64Subtarget.h#L61) is what you are suggesting?

https://github.com/llvm/llvm-project/pull/117539