This commit adds support for using a EGLDevice and EGLStreams for
rendering on top of KMS instead of gbm. It is disabled by default; to
enable it pass --enable-egl-device to configure.
By default gbm is first tried, and if it fails, the EGLDevice path is
tried. If both fails, mutter will terminate just as before.
https://bugzilla.gnome.org/show_bug.cgi?id=773629