power: supply: generic-adc-battery: Use GPIO descriptors

This driver uses platform data to pass GPIO lines using the
deprecated global GPIO numbers. There are no in-tree users
of this platform data.

Any out-of-tree or coming users of this driver can easily be
migrated to use machine descriptor tables as described in
Documentation/driver-api/gpio/board.rst
section "platform data".

Cc: Anish Kumar <anish198519851985@gmail.com>
Cc: H. Nikolaus Schaller <hns@goldelico.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>