egl: EGL_KHR_surfaceless_* extensions

egl: EGL_KHR_surfaceless_* extensions

These extensions allow an application to make a context current by
passing EGL_NO_SURFACE for the write and read surface in the call to
eglMakeCurrent.  The motivation is that applications that only want to
render to client API targets (such as OpenGL framebuffer objects)
should not need to create a throw-away EGL surface just to get a
current context.