platform/chrome: cros_ec_sensorhub: Add median filter

Events are timestamped in EC time space, their timestamps need to be
converted in host time space.

The assumption is the time delta between when the interrupt is sent
by the EC and when it is receive by the host is a [small] constant.
This is not always true, even with hard-wired interrupt. To mitigate
worst offenders, add a median filter to weed out bigger than expected
delays.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>