sensor: fxas21002: Add gyroscope driver

Adds sensor driver support for the NXP FXAS21002 3-axis gyroscope.
Includes statically configurable range and output data rate, as well as
the sensor data ready trigger.

Datasheet:
http://www.nxp.com/assets/documents/data/en/data-sheets/FXAS21002.pdf



Jira: ZEP-1392
Change-Id: I84587c4d5e76863245e9d045c6abb10b21b2615a
Signed-off-by: Maureen Helm <maureen.helm@nxp.com>