pinctrl: samsung: Hold pointer to driver data in bank struct

This patch is a preparation for converting the pinctrl-samsung driver to
one GPIO chip and IRQ domain per bank. It allows one having only
a pointer to particular bank struct to access driver data struct.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Reviewed-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Thomas Abraham <thomas.abraham@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>