gpio: bd7xxxx: Do not depend on parent driver data

The ROHM BD70528 and BD71828 GPIO drivers only need the regmap
pointer from parent. Regmap can be obtained via dev_get_regmap()
so do not require parent to populate driver data for that.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>