toytoolkit: fix new EGL extensions fallback typedefs

The dummy typedefs for "get_platform_display()" and
"create_platform_window()" were badly defined, which
prevented building Weston on older systems.

Signed-off-by: Manuel Bachmann <manuel.bachmann@open.eurogiciel.org>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>