rtc: isl1208: Support more chip variations

Add more support in the driver for dealing with differences in is1208
compatible chips.  Put the 1208, 1209, 1218, and 1219 in the list and
encode information about nvram size, tamper, and timestamp features.

This adds support for the isl1209, which has a tamper detect but no
timestamp feature.

Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Trent Piepho <tpiepho@impinj.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>