[ARM] When generating a vpaddl node the input lane type is not always the type of the
add operation since extract_vector_elt can perform an extend operation. Get the input lane
type from the vector on which we're performing the vpaddl operation on and extend or
truncate it to the output type of the original add node.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205523 91177308-0d34-0410-b5e6-96231b3b80d8