pinctrl: samsung: Constify wakeup driver specific data

Static exynos_irq_chip structures, containing driver specific data, are
referenced only through opaque data pointer in const of_device_id table.
The contents of pointed memory (exynos_irq_chip structure itself) is
then copied with kmemdup() during wakeup initialization so
exynos_irq_chip can be made const for code safenes.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>