[X86][Costmodel] Load/store i16 Stride=6 VF=2 interleaving costs

The only sched models that for cpu's that support avx2
but not avx512 are: haswell, broadwell, skylake, zen1-3

For load we have:
https://godbolt.org/z/bhscej4WM - for intels `Block RThroughput: =13.0`; for ryzens, `Block RThroughput: <=7.0`
So pick cost of `13`.

For store we have:
https://godbolt.org/z/Yf4Pfnxbq - for intels `Block RThroughput: =10.0`; for ryzens, `Block RThroughput: <=3.5`
So pick cost of `10`.

I'm directly using the shuffling asm the llc produced,
without any manual fixups that may be needed
to ensure sequential execution.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D110590