drivers: video: Add VIDEO_BUF_STARTED to poll signals

Add VIDEO_BUF_STARTED event to video_signal_result.
VIDEO_BUF_STARTED should be triggered once processing
of the buffer has started (e.g. start_of_transmission/reception)

Signed-off-by: Armin Kessler <[email protected]>

include/zephyr/drivers/video.h

@@ -142,6 +142,8 @@ enum video_endpoint_id {
 enum video_signal_result {
 	VIDEO_BUF_DONE,
 	VIDEO_BUF_ABORTED,
+	VIDEO_BUF_SOF,
+	VIDEO_BUF_EOF,
 	VIDEO_BUF_ERROR,
 };