[OpenCL] Added implicit conversion rank for overloading functions with vector data type in OpenCL
Summary: I added a new rank to ImplicitConversionRank enum to resolve the function overload ambiguity with vector types. Rank of scalar types conversion is lower than vector splat. So, we can choose which function should we call. See test for more details.
Reviewers: Anastasia, cfe-commits
Reviewed By: Anastasia
Subscribers: bader, yaxunl
Differential Revision: https://reviews.llvm.org/D30816