power: supply: z2_battery: Convert to GPIO descriptors

This converts the Palm Z2 battery driver to use GPIO descriptors.

Cc: Haojian Zhuang <haojian.zhuang@gmail.com>
Cc: Robert Jarzmik <robert.jarzmik@free.fr>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>