sparc64: switch to clockintr

sparc64: switch to clockintr

- Remove all use of timer(4/sparc64) from sparc64/clock.c.
- Don't map interrupts in timer_match(), effectively disabling
  timer(4/sparc64).  The driver will be completely removed in a
  later commit.
- Wire up tick_intrclock, stick_intrclock, and sys_tick_intrclock.
- All sparc64 machines now have a randomized statclock; stathz = hz,
  profhz = stathz * 10.

Very special thanks to miod@, without whom this would have been impossible.

sun4v testing by kmos@, mlarkin@, and kn@.  sun4u testing (%tick and the
oddball USIIe %stick) by miod@.  With input from miod@, mlarkin@, and
kettenis@.

v1: https://marc.info/?l=openbsd-tech&m=166776418803680&w=2
v2: https://marc.info/?l=openbsd-tech&m=167287772220176&w=2
v3: https://marc.info/?l=openbsd-tech&m=167322011602530&w=2

ok mlarkin@ kettenis@ miod@