Add API function pointer and ICD dispatch table definitions (#50)
Add API function pointer and ICD dispatch table definitions (#50)

...so that implementations (and others) can use definitions
straight from the headers instead of mirroring them.

The definitions come from https://github.com/KhronosGroup/OpenCL-ICD-Loader
with the following name changes:

- function pointers are now prefixed with 'cl_api_'
- the dispatch table type is now 'cl_icd_dispatch'

Contributes to https://github.com/KhronosGroup/OpenCL-ICD-Loader/issues/72

Signed-off-by: Kevin Petit <9b79a2d3df4408bbf6fcf0c9904434a8637f93cf@arm.com>
KhronosGroup/OpenCL-Headers,KhronosGroup/OpenCL-Headers