tick: don't update idle time if cpu offline

Propagate from (CR).

An offline cpu still has ts->idle_active == 1, that cause
off time is counted as idle time, and hence cause cpu load
calculated wrongly.

Check the cpu online status before updating the idle time to
fix it.

Change-Id: I8c3213105601efca037eb23ad724811b5f46d437
Signed-off-by: Lianwei Wang <a22439@motorola.com>
Reviewed-on: http://gerrit.mot.com/727323


SLTApproved: Slta Waiver <sltawvr@motorola.com>
SME-Granted: SME Approvals Granted
Tested-by: Jira Key <jirakey@motorola.com>
Reviewed-by: Igor Kovalenko <igork@motorola.com>
Submit-Approved: Jira Key <jirakey@motorola.com>