av1enc: change cpu-used range upto 5
The speed 6, 7 and 8 has been removed because it's not yet tuned correctly. https://aomedia.googlesource.com/aom/+/7ffbf92030baf6886c2486574cca16d60499bbb8
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The speed 6, 7 and 8 has been removed because it's not yet tuned correctly. https://aomedia.googlesource.com/aom/+/7ffbf92030baf6886c2486574cca16d60499bbb8