Grab the kernel lock before cleaning up single-step breakpoints.  Should prevent mips64 from hitting the same problem as found by tobiasu@ on hppa.
Grab the kernel lock before cleaning up single-step breakpoints.  Should
prevent mips64 from hitting the same problem as found by tobiasu@ on hppa.

ok miod@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars