power: goldfish_battery: add devicetree bindings

Add device tree bindings to the Goldfish virtual platform battery drivers.

Signed-off-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Jin Qian <jinqian@android.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>