* Fix test_subgroups - test as core feature.
* Fix kernels pragma in case of OpenCL 2.1 core subgroups
* Change global variable names to gVariable convention
* Allow subgroups tests execute 2 paths
- as core feature
- as extension feature
* Fix code formatting.
* Set correct OpenCL version
* Fix code format
* test_subgroups review fixes:
* do not use global variables
* make IFP as separate tests
* use stringstream data type
* use special class to load function pointer for specific API
* Remove not not used variable
* Test subgroups - use common enums
* Test subgroups - set TEST_SKIPPED_ITSELF