Get 2nd CPU to work

[Spritetm]

There's a 2nd, fully functional RiscV CPU in the SoC. At the moment, it's not really usable as the software does not support it.

• [ ] Create code to take it out of reset and have it jump to a start routine, with a stack that makes sense
• [ ] Implement spinlocks. Either in hardware or using Peterson's algorithm
• [ ] Hook up newlib lock functions, especially __malloc_lock and friends, to spinlock
• [ ] Create cross-CPU interrupts