input: sensors: add sensor class support for AKM8963

- Sensor class interface is required for sensor HAL to
  discover the sensor. This change creates sensor class
  interface for AKM8963 magnetometer sensor.
- Auto-report support added for AKM8963 driver.

CRs-fixed: 631108
Change-Id: I45dd4406a46469fe193579ee931bb266a68739e9
Signed-off-by: Prakash Gupta <guptap@codeaurora.org>