rtc: isl1208: add support for isl1219 with tamper detection

We add support for the ISL1219 chip that got an integrated tamper
detection function. This patch implements the feature by adding
an additional timestamp0 file to sysfs device path.
This file contains seconds since epoch, if an event occurred,
or is empty, if none occurred.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Denis Osterland <Denis.Osterland@diehl.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>