rtc: ds1307: enable rx8130's backup battery, make it chargeable optionally

rtc: ds1307: enable rx8130's backup battery, make it chargeable optionally

The ds1307 charger infrastructure now allows to add a rx8130 charger
setup that..

- does not depend on trickle-resistor-ohms
- does not use DS13XX_TRICKLE_CHARGER_MAGIC trickle-charge select (TCS)
  bits
- keeps previous no-charge behavior for device trees without
  aux-voltage-chargeable

Make that happen.

Signed-off-by: Bastian Krause <bst@pengutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20200917183246.19446-9-bst@pengutronix.de