cmake: fix pkg-config handling

Avoid non-intentional call of "include(FindPkgConfig)"
It should be handled in the root CMakeLists.txt (safely for cross-compiling)

cmake/OpenCVUtils.cmake

@@ -743,7 +743,7 @@ macro(ocv_check_modules define)
     endif()
     unset(${define}_${__modname}_FOUND)
   endforeach()
-  if(COMMAND pkg_check_modules)
+  if(PKG_CONFIG_FOUND OR PkgConfig_FOUND)
     pkg_check_modules(${define} ${ARGN})
   endif()
   if(${define}_FOUND)