nvdec: Create CUDA context with registered device id

Only the default device has been used by NVDEC so far.
This commit make it possible to use registered device id.
To simplify device id selection, GstNvDecCudaContext usage is removed.

sys/nvcodec/gstnvdec.h

@@ -35,25 +35,6 @@
 
 G_BEGIN_DECLS
 
-typedef struct _GstNvDecCudaContext GstNvDecCudaContext;
-typedef struct _GstNvDecCudaContextClass GstNvDecCudaContextClass;
-
-struct _GstNvDecCudaContext
-{
-  GObject parent;
-
-  CUcontext context;
-  CUvideoctxlock lock;
-};
-
-struct _GstNvDecCudaContextClass
-{
-  GObjectClass parent_class;
-};
-
-GType gst_nvdec_cuda_context_get_type (void);
-
-
 #define GST_TYPE_NVDEC          (gst_nvdec_get_type())
 #define GST_NVDEC(obj)          (G_TYPE_CHECK_INSTANCE_CAST((obj), GST_TYPE_NVDEC, GstNvDec))
 #define GST_NVDEC_CLASS(klass)  (G_TYPE_CHECK_CLASS_CAST((klass), GST_TYPE_NVDEC, GstNvDecClass))
@@ -79,9 +60,10 @@ struct _GstNvDec
   GstGLContext *gl_context;
   GstGLContext *other_gl_context;
 
-  GstNvDecCudaContext *cuda_context;
   CUvideoparser parser;
   CUvideodecoder decoder;
+  CUcontext context;
+  CUvideoctxlock ctx_lock;
 
   guint width;
   guint height;