libcamera: v4l2_device: Create device from entity name

Add a static method to V4L2Device class to create a V4L2Device instance
from a media entity name.

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

src/libcamera/include/v4l2_device.h

@@ -22,6 +22,7 @@ namespace libcamera {
 class Buffer;
 class BufferPool;
 class EventNotifier;
+class MediaDevice;
 class MediaEntity;
 
 struct V4L2Capability final : v4l2_capability {
@@ -136,6 +137,9 @@ public:
 	int streamOn();
 	int streamOff();
 
+	static V4L2Device *fromEntityName(const MediaDevice *media,
+					  const std::string &entity);
+
 protected:
 	std::string logPrefix() const;