OpenSubdiv: Refactor, move device specific code to own files

Also, move all device files to own folder.

Makes it so checks for device availability are done in a localized
place.

intern/opensubdiv/internal/device/device_context_cuda.h

@@ -0,0 +1,38 @@
+// Copyright 2020 Blender Foundation. All rights reserved.
+//
+// This program is free software; you can redistribute it and/or
+// modify it under the terms of the GNU General Public License
+// as published by the Free Software Foundation; either version 2
+// of the License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software Foundation,
+// Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+//
+// Author: Sergey Sharybin
+
+#ifndef OPENSUBDIV_DEVICE_CONTEXT_CUDA_H_
+#define OPENSUBDIV_DEVICE_CONTEXT_CUDA_H_
+
+namespace blender {
+namespace opensubdiv {
+
+class CUDADeviceContext {
+ public:
+  // Stateless check to see whether CUDA functionality is available on this
+  // platform.
+  static bool isSupported();
+
+  CUDADeviceContext();
+  ~CUDADeviceContext();
+};
+
+}  // namespace opensubdiv
+}  // namespace blender
+
+#endif  // _OPENSUBDIV_DEVICE_CONTEXT_CUDA_H_