opencl: Fix some compiler warnings [-Wunused-function]

opencl_device_selection.h contains lots of code which is only used in
openclwrapper.cpp. This results in several compiler warnings:

opencl/opencl_device_selection.h:396:18: warning:
 ‘ds_status readProfileFromFile(ds_profile*, ds_score_deserializer, const char*)’ defined but not used [-Wunused-function]
opencl/opencl_device_selection.h:257:18: warning:
 ‘ds_status writeProfileToFile(ds_profile*, ds_score_serializer, const char*)’ defined but not used [-Wunused-function]
opencl/opencl_device_selection.h:196:18: warning:
 ‘ds_status profileDevices(ds_profile*, ds_evaluation_type, ds_perf_evaluator, void*, unsigned int*)’ defined but not used [-Wunused-function]
opencl/opencl_device_selection.h:90:18: warning:
 ‘ds_status initDSProfile(ds_profile**, const char*)’ defined but not used [-Wunused-function]
opencl/opencl_device_selection.h:70:18: warning:
 ‘ds_status releaseDSProfile(ds_profile*, ds_score_release)’ defined but not used [-Wunused-function]

Move that functions and all related code to openclwrapper.cpp.

Signed-off-by: Stefan Weil <[email protected]>