iio: gyro: fxas210002c: Move exports to IIO_FXAS210002C namespace.

Includes using EXPORT_NS_GPL_DEV_PM_OPS() and the simplifications that
brings by allowing the compiler to remove unused struct dev_pm_ops
and callbacks without needing explicit __maybe_unused markings.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

--
Dropped Rui's tag on basis this is rather different from v1 due to
the different macro implementation.

v2: Switch to Paul's more flexible approach to EXPORT_NS_GPL_DEV_PM_OPS()
Acked-by: Rui Miguel Silva <rui.silva@linaro.org>
Link: https://lore.kernel.org/r/20220925155719.3316280-4-jic23@kernel.org


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