egl: make eglSwapInterval a no-op for !window surfaces

As the spec says, the function is a no-op when the surface is not a
window one.

That spec implies that EGL_TRUE should be returned in that case, yet
the ARM driver seems to return EGL_FALSE + EGL_BAD_SURFACE.

The Nvidia driver returns EGL_TRUE. We follow that behaviour until a
decision is made.

https://gitlab.khronos.org/egl/API/merge_requests/17

Cc: samiuddi <sami.uddin.mohammad@intel.com>
Cc: Erik Faye-Lund <kusmabite@gmail.com>
Cc: Tomasz Figa <tfiga@chromium.org>
Cc: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>

src/egl/main/eglapi.c

@@ -1222,6 +1222,9 @@ eglSwapInterval(EGLDisplay dpy, EGLint interval)
    if (_eglGetSurfaceHandle(surf) == EGL_NO_SURFACE)
       RETURN_EGL_ERROR(disp, EGL_BAD_SURFACE, EGL_FALSE);
 
+   if (surf->Type != EGL_WINDOW_BIT)
+      RETURN_EGL_EVAL(disp, EGL_TRUE);
+
    interval = CLAMP(interval,
                     surf->Config->MinSwapInterval,
                     surf->Config->MaxSwapInterval);