ogl: use a sample-able texture as EFB instead of renderbuffer

Renderbuffers are used to be faster for rendering, but on newer gpu generations, they internally doesn't care about renderbuffers vs textures any more. So there is no need for us to use renderbuffers which aren't as flexible as renderbuffers aren't usable as textures.
As example, interpretate format change emulation now directly sample the old msaa efb without resolving. This won't speed up (it's resolv vs sample shading), but we won't loose the MSAA sample information any more.
As CSAA is a legacy NV feature which is only compatible with renderbuffers, this feature is also removed. Also GLES3.0 doesn't support this kind of multisampled textures, but 3.1 does :D