Great utility for benchmarks, but ran into verification of unsigned c…

[stineje]

Great utility for benchmarks, but ran into verification of unsigned char from AES when comparing RISC-V crypto K extension. I apologize but I didn't know if it was okay to add this or if available elsewhere. Thank you for the great utilities as well as the awesome RISC-V community. Please feel free to delete this PR if made in error or this routine is not useful. Thank you again!