pinctrl: samsung: Constify samsung_pin_ctrl struct

In order to separate initialization constants from runtime data, this
patch modifies the driver to store only constant data in
samsung_pin_ctrl struct and copy data required at runtime to
samsung_pinctrl_drv_data struct. This makes it possible to mark all
existing instances of samsung_pin_ctrl struct as const and __initconst.

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>