STPK-1429 Add a trace warning of unusually high sysfs read times

STPK-1429 Add a trace warning of unusually high sysfs read times

It looks like some sensors (proximity on MRD 7 perhaps) have
acquisition times in the order of several hundred ms. Help
flag those with a trace warning of combined (all channels)
acquisition times larger than 100 ms. None of the T100 sensors
(magnetometer, temperature, ALS) have this problem though.

Issue: STPK-1429

Change-Id: I04ee59f63184c89eae26e46460f4dcb675b91131
Signed-off-by: Patrick Porlan <patrick.porlan@intel.com>