libretro: OpenGL support not implemented

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I'm trying to port Play! - PlayStation 2 emulator: https://github.com/rozhuk-im/game.libretro.play https://purei.org/ https://github.com/jpd002/Play-

It is compiled (with FreeBSD port system, with some private hacks) and run but Kodi (from master) crash because OpenGL in libretro not implemented.

@lrusak , @a1rwulf, @AlwinEsch , @garbear I see some progress in your git repos, but can some one make PR with this with latest changes?