Use ScaledThreshold to calculate Unroll count

[chandmudda]

Earlier we were using partial threshold to calculate unroll count for loop but for small loops it is giving more unroll count which is degrading the performance.Using Scaled Threshold improves the performance.

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[chandmudda]

@androm3da , Please suggest some reviewers who can take a look at this patch.

[androm3da]

@androm3da , Please suggest some reviewers who can take a look at this patch.

Thanks for the PR!

@fhahn or @HankChang736 might be good reviewers? They've touched the file ~recently.

[androm3da]

but for small loops it is giving more unroll count which is degrading the performance.Using Scaled Threshold improves the performance.

OBTW I've never made any real codegen changes but for the community's sake you should probably disclose the benchmark you are using here, and perhaps any other benchmarks that you think have at least neutral impact (to avoid performance regressions caused by this change).