mips64, loongson, octeon: switch to clockintr

mips64, loongson, octeon: switch to clockintr

- Remove mips64-specific clock interrupt scheduling bits from cpu_info.
- Add missing tick_nsec initialization to cpu_initclocks().
- Disable the glxclk interrupt clock on loongson.  visa@/miod@ say it
  can be removed later if it isn't useful for anything else.
- Wire up cp0_intrclock.

Notes:

- The loongson apm_suspend() changes are untested, but deraadt@ claims
  APM suspend/resume on loongson doesn't work anyway.
- loongson and octeon now have a randomized statclock(), stathz = hz.

With input from miod@, visa@.  Tested by miod@, visa@.

Link: https://marc.info/?l=openbsd-tech&m=166776379603497&w=2
ok visa@ mlarkin@