RFR: 8221092: UseAVX=3 has performance degredation on Skylake (X7) processors

[Deshpande, Vivek R]

Hi All

I have created a patch which sets AVX2 for Skylake and selectively uses EVEX instructions based on threshold
for platforms after Skylake.
I don't observe the regressions for SPECjvm2008 on Skylake with this patch.
JBS id:
https://bugs.openjdk.java.net/browse/JDK-8221092
Webrev:
http://cr.openjdk.java.net/~vdeshpande/8221092/webrev.00/
Could you all please review the patch.

Regards,
Vivek