it does not belong to anything specific - it's just a glue to window system (like GLX,WGL,AGL,etx).
and it's up to vendor to support it or no, as well as Desktop OpenGL.
If you want OpenGL 3(or higher) on ARM - only NVidia Tegra and their Jetson boards have full support of both OpenGL for Desktop and for Embeded Systems(aka ES) on Linux/arm, as well as GLX and EGL window glue. And it's hard to believe, that ARM proprietary drivers or Biforst/Mesa will have similar to Nvidia level of OpenGL support under Linux/Android (and yes, you can use Desktop OpenGL on Nvidia android tablet/tv box too ).