ogl: drop csaa support
ogl: drop NV_framebuffer_multisample_coverage
ogl: add ARB_texture_multisample
ogl: use ARB_texture_multisample for msaa
ogl: pixel format shader without resolving

v2: Don't use std::to_string as this function is broken on android.
Merge pull request #331 from degasus/kill_csaa

OpenGL: Use a sample-able texture as EFB instead of renderbuffer.