ARM: dts: fix pinctrl for s2mps11-irq on exynos5420-arndale-octa

On Arndale Octa the S2MPS11 RTC alarm interrupt was not handled
at all because of wrong configuration of interrupt and gpx3-2.
1. Interrupt is signaled by falling edge.
2. This GPIO line is hard-wired on the board to PVDD_APIO_1V8
   through a resistor so pull-up/down must be disabled.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>