Prevent users from running standlone EGL clients with wayland platform

Running standalone EGL clients with the wayland EGL platform isn't supported and it is
better to prevent us from doing so rather than crashing with a segmentation fault later.

Upstream-Status: Pending (http://github.com/libhybris/libhybris)

Signed-off-by: Simon Busch <morphis@gravedo.de>