This migrates isp1704 driver from old GPIO API to new descriptor
based GPIO API and drops useless platform data as a side-effect.

Migration is simple, since all mainline users are DT based and
DT API does not change. Out of tree users of the platform data
need to migrate to gpiod_lookup_table as described here:

Documentation/driver-api/gpio/board.rst
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>