mfd: max14577: Do not enforce (incorrect) interrupt trigger type

Interrupt line can be configured on different hardware in different way,
even inverted.  Therefore driver should not enforce specific trigger
type - edge falling - but instead rely on Devicetree to configure it.

The Maxim 14577/77836 datasheets describe the interrupt line as active
low with a requirement of acknowledge from the CPU therefore the edge
falling is not correct.

The interrupt line is shared between PMIC and charger driver, so using
level sensitive interrupt is here especially important to avoid races.
With an edge configuration in case if first PMIC signals interrupt
followed shortly after by the RTC, the interrupt might not be yet
cleared/acked thus the second one would not be noticed.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210602110445.33536-4-krzysztof.kozlowski@canonical.com