RNG using cpu timing jitter

[r4gus]

The randomness provided by the RANDOM_BIT register doesn't look that good and it depends on the clock being generated by XIP and/or PLLs.

I recently talked to somebody who maintains a library for generating random numbers using the cpu timing jitter (https://github.com/smuellerDD/jitterentropy-library). We could extract the code relevant for bare metal applications and port it to Zig. Probably requires some work but could be worth it.

Things to consider are:

1. The rng code must not be optimized
2. It depends on memory access