rtc: add rtc-driver for HID sensors of type time

This driver makes the time from HID sensors (hubs) which are offering
such available like any other RTC does.

It is necessary that all values like year, month etc, are send as
8bit values (1 byte each) and all of them in 1 report. Also the
spec HUTRR39b doesn't define the range of the year field, we
tread it as 0 - 99 because that's what most RTCs I know about are
offering.

Currently the time can only be read. Setting the time must be done
through sending a report (or a feature). The spec currently doesn't
define how and I'm not sure if I just should define something by myself.

Signed-off-by: Alexander Holler <holler@ahsoftware.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>