[X86] Explicitly list all KNL features of inheriting from IVB. NFC

I'm not sure all the microarchitectural tuning flags that have been added to IVBFeatures are relevant for KNL. Separating will allow us to see and audit them. There might even be some simplification opportunities in the Sandy Bridge through Icelake inheritance line without KNL using the same chain.

llvm-svn: 345183