Summary: try installing mesa-opencl-icd.
It's a known issue that there is currently no way for an OpenCL-using
package to ask for "the correct OpenCL driver for this hardware": it can
ask for "any OpenCL driver" (letting apt choose) or "an OpenCL driver
chosen by the packager", either of which might be the wrong one for the
user's hardware.
Debian currently has:
beignet-opencl-icd - Intel GPUs
mesa-opencl-icd - AMD/ATI GPUs (not sure exactly which ones - very new
ones might need ROCm)
pocl-opencl-icd - CPUs
Nvidia needs non-free.
I proposed [0] fixing this by creating a metapackage for "all OpenCL
drivers" (similar to the ones for graphics). However, having unusable
OpenCL drivers installed can trigger bugs: [1] in llvm, and some
applications that treat "no hardware for this driver" as "fatal error"
instead of "try the next driver".
[0]
https://alioth-lists.debian.net/pipermail/pkg-opencl-devel/Week-of-Mon-20140203/000076.html
[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=852746
