disable interrupts and loop forever with these.
- Hide all MP-related bits in <machine/smp.h> underneath #ifdef SMP.
- Inline ipi_all_but_self(9) and ipi_selected(9). We don't expose any
additional bits but save a few cycles by doing so.
- Remove ipi_all(9), which actually only called panic(9). It can't be
implemented natively anyway and having it removed at least causes
MI users to fail already fail when linking.
3664739c74