svn commit: r219676 - head/sys/x86/x86

[David Malone]

> If atomic 64-bit read/write is possible and it is absolutely 
> necessary, it has to be set via machdep.foo_freq, not 
> kern.timecounter.foo.frequency.

A number of people have asked me about adjusting the frequency of
other time counters - it would seem to make sense to allow this at
the timecounter layer. It also seems possible that people might
want the timecounters view of the frequency to be different from
other uses of a counter.

	David.