illumos gate

Unfortunately, acpi-user-options and a subset of its meanings is public and documented in for eg eeprom(8).

Disabling ACPI is largely unreasonable on modern i86pc. We should at the very least start to move away from documenting it (and the related attempt to act like the legacy acpi_intp instead of acpica).

Ideally, enable/disabling of acpi on i86pc would be a private flag for debugging purposes at most, and the legacy mode to try to act like acpi_intp would disappear entirely.

Note that we default to "disable ACPI" in two cases:
- Wx100z systems with broken firmware
- Systems with firmware dated <= 1999

So at least in theory supported systems affected by this do exist, for the On/Off toggle, though not for "legacy" acpi_intp-like behaviour.