[llvm-exegesis] Add uop computation for more X87 instruction classes.

Summary:
This allows measuring comparisons (UCOM_FpIr32,UCOM_Fpr32,...),
conditional moves (CMOVBE_Fp32,...)

Reviewers: gchatelet

Subscribers: tschuett, llvm-commits

Differential Revision: https://reviews.llvm.org/D48713

llvm-svn: 336352