Integrate `embench-iot` for benchmarking

[jserv]

Embench benchmark suite is designed to test the performance of deeply embedded systems.

• The measurement of execution performance is designed to use "hot" caches. Thus each benchmark executes its entire code several times, before starting a timing run.
• Execution runs are scaled to take approximately 4 second of CPU time. This is large enough to be accurately measured, yet means all benchmarks, including cache warm up can be run in a few minutes.
• To facilitate execution on machines of different performance, the tests are scaled by the clock speed of the processor.

[jserv]

riscv-benchmark-automation provides the necessary changes to adopt embench-iot for RISC-V.

[jserv]

@fourcolor, can you make a list for known pending issues to evaluate embench-iot?