iio: imu: lsm6dsx: Use new pm_sleep_ptr() and EXPORT_SIMPLE_DEV_PM_OPS()

These new functions move the burden of removing unused code when
CONFIG_PM_SLEEP is not defined onto the compiler rather than requiring
the use of CONFIG_PM guards and similar.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/20220220181522.541718-8-jic23@kernel.org


Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/20220604161223.461847-5-jic23@kernel.org