libcamera: FrameBuffer: Add a method to copy buffer content

This method may be used to memory copy a whole FrameBuffer content
from another buffer. The operation is not fast and should not be used
without great care by pipelines.

The intended use-case is to have an option to copy out RAW buffers from
the middle of a pipeline.

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

include/libcamera/buffer.h

@@ -57,6 +57,7 @@ public:
 	unsigned int cookie() const { return cookie_; }
 	void setCookie(unsigned int cookie) { cookie_ = cookie; }
 
+	int copyFrom(const FrameBuffer *src);
 private:
 	friend class Request; /* Needed to update request_. */
 	friend class V4L2VideoDevice; /* Needed to update metadata_. */