GMIN-2992: Revisit gyroscope calibration

GMIN-2992: Revisit gyroscope calibration

Modify the code so it provides valid uncalibrated gyro samples
while calibrating (we simply use bias 0 until we can determine
it), and compute bias iteratively (no need for long term sample
storage).

I can now pass the Cts Verifier gyroscope measurement test
effortlessly, and the delayed calibration is also visible in
applications such as Sensor Readout.

Issue: GMIN-2992

Change-Id: I7d86c529da0167e72ab93039d370f2df1c058ab3
Signed-off-by: Patrick Porlan <patrick.porlan@intel.com>