cam: drm: Set per-plane offsets when creating DRM frame buffer

Now that libcamera supports per-plane offsets, pass the values to
drmModeAddFB2(). The KMS sink in cam is now capable of rendering
multi-planar formats.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/cam/drm.cpp

@@ -623,7 +623,7 @@ std::unique_ptr<FrameBuffer> Device::createFrameBuffer(
 		fb->planes_.push_back({ handle });
 
 		handles[i] = handle;
-		offsets[i] = 0; /* TODO */
+		offsets[i] = plane.offset;
 		++i;
 	}