x86/time: change initiation of the calibration timer

x86/time: change initiation of the calibration timer

Setting the timer a second (EPOCH) into the future at a random point
during boot (prior to bringing up APs and prior to launching Dom0) does
not yield predictable results: The timer may expire while we're still
bringing up APs (too early) or when Dom0 already boots (too late).
Instead invoke the timer handler function explicitly at a predictable
point in time, once we've established the rendezvous function to use
(and hence also once all APs are online). This will, through the raising
and handling of TIMER_SOFTIRQ, then also have the effect of arming the
timer.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Release-Acked-by: Ian Jackson <iwj@xenproject.org>