CpuMath Enhancement: Preamble for hardware intrinsics implementation

[briancylui]

Style changes needed to solve part of #823

Details

• Do "preamble" for the implementation of SSE/AVX intrinsics in src\Microsoft.ML.CpuMath\SseIntrinsics.cs and src\Microsoft.ML.CpuMath\AvxIntrinsics.cs:

Preamble:

1. while (!aligned) { do scalar operation; } // preamble
2. Do vectorized operation using ReadAligned
3. while (!end) { do scalar operation; }
   For large arrays, especially those that cross cache line or page boundaries, doing this should save some measurable amount of time.

Reference: https://github.com/dotnet/machinelearning/pull/562/files/f0f81a5019a3c8cbd795a970e40d633e9e1770c1#r204061074
#1143

Currently these functions are just using Unaligned Loads, we can make them after by aligning the data and doing aligned loads.

• AddScalerU
• ScaleSrcU
• AddScaleU
• ScaleAddU
• AddU
• AddScaleCopyU
• AddSU
• MulElementWiseU
• SumU
• SumSqU
• SumSqDiffU
• SumAbsU
• SumAbsDiffU
• MaxAbsU
• MaxAbsDiffU
• DotU
• DotSU
• Dist2
• SdcaL1UpdateU
• SdcaL1UpdateSU