gpio: of: remove of_gpiochip_and_xlate() and struct gg_data

The usage of gpiochip_find(&gg_data, of_gpiochip_and_xlate) is odd.

Usually gpiochip_find() is used to find a gpio_chip.  Here, however,
the return value from gpiochip_find() is just discarded.  Instead,
gpiochip_find(&gg_data, of_gpiochip_and_xlate) is called for the
side-effect of the match function.

The match function, of_gpiochip_find_and_xlate(), fills the given
struct gg_data, but a match function should be simply called to
judge the matching.

This commit fixes this distortion and makes the code more readable.
Remove of_gpiochip_find_and_xlate() and struct gg_data.  Instead,
this adds a very simple helper function of_find_gpiochip_by_node().
Now, of_get_named_gpiod_flags() is implemented more straight-forward.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>