cam: Cache buffer memory mapping

With the buffer allocator in use it's possible to cache the dmabuf
memory mappings when starting the camera instead of mapping and
unmapping them each time.

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

src/cam/capture.cpp

@@ -116,6 +116,9 @@ int Capture::capture(EventLoop *loop, FrameBufferAllocator *allocator)
 					  << std::endl;
 				return ret;
 			}
+
+			if (writer_)
+				writer_->mapBuffer(buffer.get());
 		}
 
 		requests.push_back(request);