pinctrl: exynos: Generalize the eint16_31 demux code

The function exynos_irq_demux_eint16_31 uses pre-defined offsets for external
interrupt pending status and mask registers. So this function is not extensible
for Exynos7 SoC which has these registers at different offsets. Generalize
the exynos_irq_demux_eint16_31 function by using the pending/mask register
offset values from the exynos_irq_chip structure. This is done by adding a
irq_chip field to the samsung_pin_bank struct.

Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Reviewed-by: Thomas Abraham <thomas.ab@samsung.com>
Tested-by: Thomas Abraham <thomas.ab@samsung.com>
Acked-by: Tomasz Figa <tomasz.figa@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>