libcamera: pipeline_handler: Add functions to lock a whole pipeline

Add lock() and unlock() which are backed by the MediaDevice
implementation and lock all media devices claimed by a pipeline handler
instance.

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

src/libcamera/include/pipeline_handler.h

@@ -57,6 +57,9 @@ public:
 	MediaDevice *acquireMediaDevice(DeviceEnumerator *enumerator,
 					const DeviceMatch &dm);
 
+	bool lock();
+	void unlock();
+
 	virtual CameraConfiguration
 	streamConfiguration(Camera *camera, const std::vector<StreamUsage> &usages) = 0;
 	virtual int configureStreams(Camera *camera, const CameraConfiguration &config) = 0;