drivers: sensors: Add sysfs property to read QDSP timer

Add a sysfs entry for SSC sensor device to read QDSP timer.
Time is read from QDSP timer, which is used to synchronize
with the QDSP.

CRs-fixed: 1087711
Signed-off-by: Haihe Zhang <haihez@codeaurora.org>
Change-Id: Idc91244818c2f0358e5b3e7ec907637d81acd2f4