ARM: dts: exynos: correct PMIC interrupt trigger level on Rinato

The Samsung PMIC datasheets describe the interrupt line as active low
with a requirement of acknowledge from the CPU.  Without specifying the
interrupt type in Devicetree, kernel might apply some fixed
configuration, not necessarily working for this hardware.

Fixes: faaf348e ("ARM: dts: Add board dts file for exynos3250-rinato")
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20201210212903.216728-3-krzk@kernel.org