[X86] Merged Reverse/Alternate shuffle cost tables. NFCI.

As discussed on D27811, merged the shuffle cost LUTs and use the shuffle kind to perform the lookup instead of the ISD opcode.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290956 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed