Use fdinfo's engine count when refreshing utilisation rate

[larunbe]

I originally moved gpuinfo_refresh_utilisation_rate() from Mali code into src/extract_gpuinfo.c when I realised utilisation rate could be calculated in a device-independent way simply by following the percentage utilisation guidelines given in Documentation/gpu/drm-usage-stats.rst

However, I forgot to replace the magic number '2' which stood for the engine count in Mali GPUs with a value that make sense for different devices.

Source the engine count from gpu_info's static information values.

[chealy]

+1

[Syllo]

Thanks for the patch!