Move libcudart and libopencl dependencies from libnanox (core) to arch plugins

Current nanox version is forced to link its core library (libnanox.so) with both cuda and opencl. This forces the user program to load those libraries even if it does not make use of any cuda or opencl tasks.

This requirement also increases the complexity of the build process.

If Cuda and OpenCL API calls are restricted to their corresponding plugins, this restriction would disappear.