[X86][AVX][AVX2]: Adding full coverage of MC encoding for the AVX, AVX2 isa set.<NFC>

NFC.
Adding MC regressions tests to cover the AVX and AVX2 ISA sets.
This patch is part of a larger task to cover MC encoding of all X86 ISA Sets.
See revision: https://reviews.llvm.org/D39952

Reviewers: zvi, RKSimon, aymanmus, m_zuckerman
Differential Revison: https://reviews.llvm.org/D40287

Change-Id: I304687a2b7abb473f79de99c31fc55c97b2662da
llvm-svn: 320716