Compat for opencl mode between cpu mode and gpu mode (#655)

some host opencl runtime may at cpu mode, but remote

client opencl runtime at gpu mode, compat it

CONTRIBUTORS.md

@@ -35,3 +35,4 @@ List of Contributors
 - [Qiao Zhang](https://github.com/zhangqiaorjc)
 - [Jian Weng](https://github.com/were)
 - [Masahiro Masuda](https://github.com/masahi)
+- [Haolong Zhang](https://github.com/haolongzhangm)

src/runtime/opencl/opencl_device_api.cc

@@ -197,8 +197,13 @@ void OpenCLWorkspace::Init() {
   std::vector<cl_device_id> devices_matched =
       cl::GetDeviceIDs(this->platform_id, "gpu");
   if (devices_matched.size() == 0) {
-    LOG(WARNING) << "No OpenCL device any device matched given the options";
-    return;
+    LOG(WARNING) << "No OpenCL device any device matched given the options: gpu mode";
+    LOG(WARNING) << "Now try OpenCL cpu mode";
+    devices_matched = cl::GetDeviceIDs(this->platform_id, "cpu");
+    if (devices_matched.size() == 0) {
+      LOG(WARNING) << "No OpenCL device any device matched given the options: cpu mode";
+      return;
+    }
   }
   this->devices = devices_matched;
   cl_int err_code;