Add device_hw_t and device_v4l2_open

device/v4l2/device.c

@@ -0,0 +1,9 @@
+#include "device/hw/v4l2.h"
+#include "device/hw/device.h"
+
+extern device_hw_t device_hw_v4l2;
+
+device_t *device_v4l2_open(const char *name, const char *path)
+{
+  return device_open(name, path, &device_hw_v4l2);
+}