[ARM] Factor out two-result shuffle matching.  NFCI.

In preparation for a future patch: makes it easier to do the same
matching to generate different nodes, without duplication.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240116 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed