PR port-sparc/54789: Sparc boot fails with "Trap 0x21 while interrupts disabled"

Remove assumption that cpu_info is smaller than 1kB.

Add apc(4), a driver for the Aurora Personality Chip (APC) found
on SPARCstation-4/5, and emulated by qemu to idle the simulator
when the CPU is idle. Infos about the registers from the linux driver.

Add apc(4), a driver for the Aurora Personality Chip (APC) found
on SPARCstation-4/5, and emulated by qemu to idle the simulator
when the CPU is idle. Infos about the registers from the linux driver.
Not enabled by default because it can cause some Sparc systems to
hang (so says the linux driver).
Only the CPU idle part implemented at this time; fan speed and
Convenience power outlet management to be added.
Tested on qemu.

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