libcamera: formats: Add toString() methods

Add toString() helpers to pretty print out a V4L2Device or V4L2Subdevice
format.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>

src/libcamera/include/v4l2_device.h

@@ -100,6 +100,8 @@ public:
 		uint32_t bpl;
 	} planes[3];
 	unsigned int planesCount;
+
+	const std::string toString() const;
 };
 
 class V4L2Device : protected Loggable

src/libcamera/include/v4l2_subdevice.h

@@ -21,6 +21,8 @@ struct V4L2SubdeviceFormat {
 	uint32_t mbus_code;
 	uint32_t width;
 	uint32_t height;
+
+	const std::string toString() const;
 };
 
 class V4L2Subdevice : protected Loggable