Make pyopencl fit for OpenCL 3.1

[Friedrich2]

The Khronos Group has announced the release of OpenCL 3.1. This ticket is intended to serve as a collector for others for all necessary overhauls (behavioural changes, optimizations as well as source code refactoring) originating from this, if there are any.
Changes within the spec are collected here.

[inducer]

Thanks for opening this. It's been on my radar, but since there aren't any implementations just yet, it's not immensely high-priority for me. Help (in the form of PRs) is welcome though!