libcamera: v4l2_device: Add method to lookup device path

Add a method to lookup a V4L2 devices path in sysfs.

Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

include/libcamera/internal/v4l2_device.h

@@ -30,6 +30,7 @@ public:
 	int setControls(ControlList *ctrls);
 
 	const std::string &deviceNode() const { return deviceNode_; }
+	std::string devicePath() const;
 
 protected:
 	V4L2Device(const std::string &deviceNode);