i2c: Add Microcrystal RV3032 RTC driver

This is a simple RTC driver for the rv3032 from Microcrystal.
Just the basic functionality is implemented (no timer, alarm etc ..).

Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D41995

(cherry picked from commit 1d6a6a524409662992ca96bc91ae69b2a2a5ff35)