ocl: avoid unnecessary loading/initializing OpenCL subsystem

If there are no OpenCL/UMat methods calls from application.

OpenCL subsystem is initialized:
- haveOpenCL() is called from application
- useOpenCL() is called from application
- access to OpenCL allocator: UMat is created (empty UMat is ignored) or UMat <-> Mat conversions are called

Don't call OpenCL functions if OPENCV_OPENCL_RUNTIME=disabled
(independent from OpenCL linkage type)

modules/core/src/trace.cpp

@@ -8,6 +8,8 @@
 #include <opencv2/core/utils/trace.private.hpp>
 #include <opencv2/core/utils/configuration.private.hpp>
 
+#include <opencv2/core/opencl/ocl_defs.hpp>
+
 #include <cstdarg> // va_start
 
 #include <sstream>
@@ -596,7 +598,7 @@ void Region::destroy()
 #endif
 #ifdef HAVE_OPENCL
         case REGION_FLAG_IMPL_OPENCL:
-            if (param_synchronizeOpenCL && cv::ocl::useOpenCL())
+            if (param_synchronizeOpenCL && cv::ocl::isOpenCLActivated())
                 cv::ocl::finish();
             myCodePath = Impl::CODE_PATH_OPENCL;
             break;