pinctrl: samsung: Remove legacy API for handling external wakeup interrupts mask

Remove the legacy, ugly API of exposing the static value of external
wakeup interrupts mask, because all arch-machine users where converted
to use generic implementation from pinctrl driver.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Tomasz Figa <tomasz.figa@gmail.com>
Cc: Sylwester Nawrocki <snawrocki@kernel.org>
Acked-by: Tomasz Figa <tomasz.figa@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>