ds1307: add support for the EPSON RX-8035SA I2C RTC

The EPSON RX-8035SA I2C RTC has a similar time register layout to the
ds1307 family, with some minor differences in bit positions, polarity
and control registers. Further generalize ds1307 to make it easier
to add more compatible chips and add support for the EPSON RX-8035SA.

MFC after: 6 days
Sponsored by: Traverse Technologies
Differential Revision: https://reviews.freebsd.org/D35837