Use automatic bindings for rust-egl

[emilio]

rust-egl is unmaintained, and not all the possible bindings are there, using automatic bindings could be a good option to make it more consistent with other repos like rust-glx.

It will require to update:

• layers
• ports/gonk
• ports/glutin

Most of the refactoring will just be unsafe {} wrappers and changing constants from egl::EGL_XX to egl::XX, so won't be such an amount of work.

cc @glennw

[dralley]

I think the only thing still using this is libmlservo