Use the OpenCL dispatch defnitions from OpenCL_Headers

https://github.com/KhronosGroup/OpenCL-Headers/pull/50 added a new header file, CL/cl_icd.h, that exports the typedef for all entry points, as well as a structure for the actual dispatch table.

This allows removing the hardcoded dispatch table in src/gallium/state_trackers/clover/api/dispatch.hpp.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information