dt-bindings: rtc: ds1307: add rx8130 aux-voltage-chargeable support

Epson's RX8130 was not charged before. A related patch will allow
optional charging.
Signed-off-by: Bastian Krause <bst@pengutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200917183246.19446-4-bst@pengutronix.de

Documentation/devicetree/bindings/rtc/rtc-ds1307.txt

@@ -31,7 +31,7 @@ Optional properties:
 	Selected resistor for trickle charger
 	Possible values are 250, 2000, 4000
 	Should be given if trickle charger should be enabled
-- aux-voltage-chargeable: ds1339, ds1340 and ds1388 only
+- aux-voltage-chargeable: ds1339, ds1340, ds1388 and rx8130 only
 	Tells whether the battery/supercap of the RTC (if any) is
 	chargeable or not.
 	Possible values are 0 (not chargeable), 1 (chargeable)