power: supply: ab8500: Convert to dev_pm_ops

Switch over to using generic dev_pm_ops since these
drivers aren't even using the special power state passed
to the legacy call.

Cc: Marcus Cooper <codekipper@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>