[llvm] [AArch64] Override isLSRCostLess, take number of instructions into account (PR #84189)

[Paul Walker via llvm-commits]

https://github.com/paulwalker-arm approved this pull request.

This looks like a good change to me.  I'm happy to trust you'll do the right thing if your performance runs suggest otherwise.

https://github.com/llvm/llvm-project/pull/84189