iio: cros_ec: Relax sampling frequency before suspending

If an application set a tight sampling frequency, given the interrupt
use is a wakeup source, suspend will not happen: the kernel will receive
a wake up interrupt and will cancel the suspend process.

Given cros_ec sensors type is non wake up, this patch adds prepare and
complete callbacks to set 1s sampling period just before suspend. This
ensures the sensor hub will not be a source of interrupt during the
suspend process.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>