sbs-battery: Add dt to power_supply struct

By passing in the dt node of this device, we enable the logic for linking
power_supplies together from dt. This is specified by adding a
"power-supplies" property with a phandle to the charger for a given
supply.

Enable this logic now for the sbs-battery driver.

Signed-off-by: Rhyland Klein <rklein@nvidia.com>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>