Improve startup time with qemu

[fhunleth]

This system starts up amazingly slowly in qemu. It looks like there's some low hanging fruit:

1. Turn off jitter entropy since its jitter calibration routine hogs the CPU at boot. Jitter entropy doesn't seem like it adds value for the qemu use case anyway.
2. Will updating the qemu script to use >1 processor help?
3. Boot prints appear to scroll slowly. Is qemu doing anything to slow them down? Perhaps we should just turn them off.

[SteffenDE]

Just for comparison: amazingly slowly means 25 seconds for me on an x86 machine, 30s on an M1 MacBook emulating x86.

[fhunleth]

Thanks for adding the timings. I really expected startup time to be in the low seconds. This really surprised me.