libavfilter/dnn: add layout option to openvino backend

Dnn models have different input layout (NCHW or NHWC), so a
"layout" option is added
Use openvino's API to do layout conversion for input data. Use swscale
to do layout conversion for output data as openvino doesn't have
similiar C API for output.

Signed-off-by: Wenbin Chen <wenbin.chen@intel.com>

libavfilter/dnn_interface.h

@@ -56,12 +56,19 @@ typedef enum {
     DFT_ANALYTICS_CLASSIFY, // classify for each bounding box
 }DNNFunctionType;
 
+typedef enum {
+    DL_NONE,
+    DL_NCHW,
+    DL_NHWC,
+} DNNLayout;
+
 typedef struct DNNData{
     void *data;
     int width, height, channels;
     // dt and order together decide the color format
     DNNDataType dt;
     DNNColorOrder order;
+    DNNLayout layout;
 } DNNData;
 
 typedef struct DNNExecBaseParams {