simple-egl: HACK to report presentation flags

simple-egl: HACK to report presentation flags

So that we can test the per-surface ZERO_COPY flag:
- start Weston on DRM backend
- run ./weston-simple-egl -o (need to be opaque to end up on overlay)
- hit debug key 'V' to enable the (broken) hw overlays

The debug key is used by first hitting Mod+Shift+space, then hitting 'v'.

Enabling overlays should change the flags from 0x7 to 0xe. To verify the
window is really on an overlay, use debug key 'S' to tint all
GL-composited things green.

This patch is not intended for upstream.

Reviewed-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Tested-by: Mario Kleiner <mario.kleiner.de@gmail.com>