[TTI][X86] Reordered getCmpSelInstrCost cost tables in descending ISA order. NFCI.

Minor tidyup to make it clearer whats going on before adding additional costs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@351683 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed