[X86][SSE] Pull out target shuffle resolve code into helper. NFCI.

Pulled out code that removed unused inputs from a target shuffle mask into a helper function to allow it to be reused in a future commit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293175 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed