evas-wayland-egl: Fix evas wayland_egl engine crash on mesa driver

evas-wayland-egl: Fix evas wayland_egl engine crash on mesa driver

Summary:
Evas wayland_egl engine crashes on startup when it is running with mesa.
Evas is trying to get EGL / GLES extension function addresses where evas_gl_symbols.
It is called before eglGetDisplay. Then mesa considers that current egl platform is
X11 if it has no EGL_PLATFORM env var. This behavior of mesa is bad. But we should
provide workaround until it is fixed. Thus EGL_PLATFORM env var should be defined to
wayland before calling eglGetProcAddress.
@fix

Test Plan: run elementary_test under wayland with wayland_egl engine.

Reviewers: raster, stefan_schmidt, devilhorns

Reviewed By: devilhorns

Subscribers: cedric

Differential Revision: https://phab.enlightenment.org/D1312