Fix incorrect variable names/variables being stored in cache.

This also adds OpenCL_VERSION_MAJOR and OpenCL_VERSION_MINOR to
the list of found variables.
Add FindOpenCL module
Merge topic 'add-FindOpenCL' into next

796d77f5 Fix incorrect variable names/variables being stored in cache.
FindOpenCL: Format rst docs
Merge topic 'add-FindOpenCL' into next

6284d674 FindOpenCL: Format rst docs
Merge topic 'add-FindOpenCL' into next

041485bc Add FindOpenCL module