Hello, it looks to me like glmark2 is correctly reporting the gl vendor as ARM and the the Mail GPU device. glxinfo, on the other hand is reporting Mesa/X.org and the llvmpipe renderer. It looks like your board does not have hardware accelerated GLX support. It is most likely that there are no GLX implementations for ARM GPUs.
Try EGL instead, right now VTK does not have an onscreen EGL window, so you can take rendered image from the VTK EGL render window and show them in your device.