sensor: Implement driver and tests for akm09918c

Add the implementation for the akm09918c magnetometer driver.
Additionally, add the appropriate node to the TDK robokit1 device
tree. In order to prevent regressions, add the sensor to the sensor
build_all tests and specific tests using an emulator.

Signed-off-by: Yuval Peress <peress@google.com>
17 files changed