fix RCSIDs.

initclocks() now fixes up tick and tickadj if hz changes, so we no
longer need to do it.

- qemu_hardclock(): fix check for spurious hardclock call.
- qemu_clock_init(): Initialize qemu_nsec_per_tick *after* adjusting hz.
Error pointed out by Jonathan Kollasch.

Provide an alternate delay function that uses the Qemu get-time hypercall.

Improve time keeping and host CPU usage when running in Qemu:
- clockattach(): Allow multiple calls when running in Qemu. Anything
after this first one is ignored, but this gives us a change to use
a clock source provided by the VM directly, rather than relying on
a more expensive hardware emulation.
- Add cpu_initclocks_secondary(), to handle clock setup on secondary
CPUs, if needed.
- Allow us to use the WTINT PALcode call in cpu_idle() to idle in a lower
power state (Qemu's PALcode supports this).
- Use the Qemu per-cpu set-alarm-rel call as the hardclock interrupt
source. In Qemu environments, reduce hz to 50 (rather than the
default 1024) to give the clock a snowball's chance when running on
a host system with hz=100. XXX We have to manually re-calculate
tick and tickadj. There should be MI code to do this for us. Also
in Qemu environments, let hardclock() drive the sched clock by setting
schedhz=0.

Add a "qemu" driver to access services provided by the Qemu VM. First
order of business is to use the Qemu "get-time" console service call as
the perferred system timecounter.