KVM: PPC: use ticks, not usecs, for exit timing

Convert to microseconds when displaying
(with fix from Bharat Bhushan <Bharat.Bhushan@freescale.com>).

This reduces rounding error with large quantities of short exits.

Signed-off-by: Stuart Yoder <stuart.yoder@freescale.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>