regulator: tps65910: Add backup battery regulator

tps65910 has a backup battery charger with a configurable voltage. This
patch adds a regulator for the backup battery.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Mark Brown <broonie@linaro.org>

diff --cc Documentation/devicetree/bindings/mfd/tps65910.txt
Simple merge

diff --cc drivers/regulator/tps65910-regulator.c
Simple merge

diff --cc include/linux/mfd/tps65910.h
Simple merge