iio: common: cros_ec_sensors: Add label attribute

When sensor location is known, populate iio sysfs "label" attribute:

* "accel-base" : the sensor is in the base of the convertible (2-1)
  device.
* "accel-display" : the sensor is in the lid/display plane of the
  device.
* "accel-camera" : the sensor is in the swivel camera subassembly.

The non-standard |location| attribute is removed, the field |loc| in
cros_ec_sensors_core_state is removed.

It apply to standalone accelerometer as well as IMU (accelerometer +
gyroscope) and sensors where the location is known (light).

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Link: https://lore.kernel.org/r/20220427190804.961697-3-gwendal@chromium.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>