clients: Support explicit synchronization in simple-dmabuf-egl

Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>

Changes in v7:
  - Merge acquire fence and release fence code blocks in redraw().
  - Use 1 << n to define option bitflags.
  - Remove redundant statement involving OPT_IMPLICIT_SYNC.

Changes in v6:
  - Add option for window size.
  - Add option for enabling/disabling explicit sync.

Changes in v5:
  - Meson support.