This Embedded Controller has an internal RTC that is exposed
as a standard RTC class driver with read/write functionality.

The driver is added to the drivers/rtc/ so that the maintainer of that
directory will be able to comment on this change, as that maintainer is
the expert on this system. In addition, the driver code is called
indirectly after a corresponding device is registered from core.c,
as opposed to core.c registering the driver callbacks directly.

To test:
> hwclock --show --rtc /dev/rtc1
2007-12-31 16:01:20.460959-08:00
> hwclock --systohc --rtc /dev/rtc1
> hwclock --show --rtc /dev/rtc1
2018-11-29 17:08:00.780793-08:00

> hwclock --show --rtc /dev/rtc1
2007-12-31 16:01:20.460959-08:00
> hwclock --systohc --rtc /dev/rtc1
> hwclock --show --rtc /dev/rtc1
2018-11-29 17:08:00.780793-08:00
Signed-off-by: NDuncan Laurie <dlaurie@google.com>
Signed-off-by: NNick Crews <ncrews@chromium.org>
Acked-by: NAlexandre Belloni <alexandre.belloni@bootlin.com>
[Fix the sparse warning: symbol 'wilco_ec_rtc_read/write' was not declared]
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: NEnric Balletbo i Serra <enric.balletbo@collabora.com>