pinctrl: samsung: Include bank-specific eint offset in bank struct

Some SoCs, like Exynos4x12, have non-sequential layout of EINT control
registers and so current way of calculating register addresses does not
work correctly for them.

This patch adds eint_offset field to samsung_pin_bank struct and
modifies the driver to use it instead of calculating the offsets from
bank index.

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>