gpio: regmap: move drvdata to config data

Drop gpio_regmap_set_drvdata() and instead add it to the configuration
data passed to gpio_regmap_register().

gpio_regmap_set_drvdata() can't really be used in a race free way. This
is because the gpio_regmap object which is needed by _set_drvdata() is
returned by gpio_regmap_register(). On the other hand, the callbacks
which use the drvdata might already be called right after the
gpiochip_add() call in gpio_regmap_register(). Therefore, we have to
provide the drvdata early before we call gpiochip_add().

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>