[X86][SLM] Keep similar scheduler costs types together. NFCI.

The SLM model is inconsistent about where it kept its 'unsupported' schedule classes - better to keep them close to similar classes.

I'm not sure why some ymm classes are defined and others are unsupported though (but I haven't altered them) - the only SLM-like CPU supporting any ymm is KNL and that currently uses the HSW model.