ocl: fix for get string info from OpenCL
perf: added simple collection strategy
ocl::cvtColor works with ROI properly
some optimization of binary ocl::bitwise operations
misprint in disabling ocl::svm
Merge pull request #1616 from ilya-lavrenov:ocl_cvtColor
Merge pull request #1609 from ilya-lavrenov:ocl_some_optimization
Merge pull request #1612 from alalek:ocl_fix_string_info
Merge pull request #1614 from ilya-lavrenov:ocl_svm_misprint
demonstrative device info output
Fixed typo in document.

Signed-off-by: Han Qiang <a0byte@gmail.com>
Merge pull request #1617 from ilya-lavrenov:ocl_info
Merge pull request #1573 from alalek:perf_simple_strategy
Merge pull request #1622 from a0byte:2.4
Let btvRegWeights to be constant per `process` call.
Let Farneback to be the default optical flow method.
clean up superres btv1 ocl kernel file
Remove unused functions.
Fix a timing method bug for ocl path.
Remove useless finish operation in farneback