[NFC][llvm-exegesis] Also promote getSchedClassPoint() into ResolvedSchedClass.

Summary:
It doesn't need anything from Analysis::SchedClassCluster class,
and takes ResolvedSchedClass as param, so this seems rather fitting.

Reviewers: courbet, gchatelet

Reviewed By: courbet

Subscribers: tschuett, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59994

llvm-svn: 357263