Comment 9 for bug 1401390

nvidia-331 recommends nvidia-prime, which is needed in order to get hybrid graphics to work.

This said, I've just found out that simply rebuilding hwloc generates a libhwloc-plugins package with the correct dependencies:

Depends: libc6 (>= 2.4), libltdl7 (>= 2.4.2), libopencl-1.1-1, libpciaccess0, libxml2 (>= 2.7.4), ocl-icd-libopencl1 (>= 1.0) | libopencl1, libhwloc5

This will make sure that libhwloc-plugins does the right thing by pulling in ocl-icd-libopencl1.