ARM: exynos: Remove legacy setting of external wakeup interrupts

Since Exynos/S5Pv210 pin-controller driver is taking care about setting
the external wakeup interrupts mask, the legacy code can be removed.

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>