dt-bindings: power: supply: ab8500: Standard monitored-battery

Make monitored-battery the standard phandle to the battery we monitor
for the AB8500 charger components. We make the old "battery" phandle
deprecated, and the new one required so we detect and fix all users to
use the standard phandle name.

Cc: devicetree@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>