OpenCL: use the new library loading architecture for all OpenCL code.

An OpenCL SDK is no longer needed to build OpenCL support.
Note: as a result, the --enable-opencl configure option is removed.

Also, libOpenCL is no longer needed to run the application (it is still necessary to use OpenCL features, of course).



git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5886 b64f7644-9d1e-0410-96f1-a4d463321fa5