perf: allow parsing of job sizes as list

Job sizes can be passed now as a list of sizes and not just a single value
or a range.

Example (run benchmark with buffer sizes of 84B, 256B and 1280B):

./perf/ipsec_perf --cipher-algo aes-docsis-128 --hash-algo docsis-crc32 \
                  --job-size 84,256,1280 --job-iter 3000000 \
                  -o 0 --arch AVX512