event: Support a simple spy record

The current event spy is always passed the event context and the event.
The context is always NULL for a static spy. The event is not often used.

Introduce a 'simple' spy which takes no arguments. This allows us to drop
the adaptation code that many of these spy records use.

Update the event script to find these in the image.

Signed-off-by: Simon Glass <sjg@chromium.org>