dnn: allow setting IE paths via command line

cmake/OpenCVDetectInferenceEngine.cmake

@@ -30,7 +30,7 @@ if(NOT INF_ENGINE_ROOT_DIR OR NOT EXISTS "${INF_ENGINE_ROOT_DIR}/include/inferen
         list(APPEND ie_root_paths "${INTEL_CVSDK_DIR}/inference_engine")
     endif()
 
-    if(WITH_INF_ENGINE AND NOT ie_root_paths)
+    if(NOT ie_root_paths)
         list(APPEND ie_root_paths "/opt/intel/deeplearning_deploymenttoolkit/deployment_tools/inference_engine")
     endif()
 

modules/dnn/CMakeLists.txt

@@ -80,7 +80,7 @@ else()
   set(sources_options EXCLUDE_OPENCL)
 endif()
 
-if(WITH_INF_ENGINE AND HAVE_INF_ENGINE)
+if(HAVE_INF_ENGINE)
   add_definitions(-DHAVE_INF_ENGINE=1)
   list(APPEND include_dirs ${INF_ENGINE_INCLUDE_DIRS})
   list(APPEND libs ${INF_ENGINE_LIBRARIES})