[VectorUtils] add funnel-shifts to the list of vectorizable intrinsics

This just identifies the intrinsics as candidates for vectorization.
It does not mean we will attempt to vectorize under normal conditions
(the test file is forcing vectorization). 

The cost model must be fixed to show that the transform is profitable 
in general.

Allowing vectorization with these intrinsics is required to avoid
potential regressions from canonicalizing to the intrinsics from
generic IR:
https://bugs.llvm.org/show_bug.cgi?id=37417

llvm-svn: 346661