[X86][AVX512F_SCALAR]: Adding full coverage of MC encoding for the AVX512F_SCALAR isa sets. NFC

Adding MC regressions tests to cover the AVX512F_SCALAR isa sets.
This patch is part of a larger task to cover MC encoding of all X86 isa sets started in revision: https://reviews.llvm.org/D39952

Differential Revision: https://reviews.llvm.org/D41174

llvm-svn: 351874