input: sensors: report accurate timestamp on apds993x driver

Reporting accurate timestamp provides better reference to
sensor application. As input system will ignore sensor event
if its value doesn't change, report accurate timestamp along
with sensor event to allow input system report each sensor
event.

CRs-fixed: 778265
Change-Id: I99aaf1f1a6c275d58c71974d1f75668b3b8c86d0
Signed-off-by: Bingzhe Cai <bingzhec@codeaurora.org>