egl: simplify dri2_initialize_*()
eglInitialize()
already handles the "retry using the software path" logic, there's no need to repeat it in every platform's initialization function.
We could go the other way and drop the logic from eglInitialize()
and instead make sure every platform does it locally, but this way is makes the code simpler (if maybe a bit less optimized as it unrolls a quite bit on some platforms before trying again).