mfd: da9062: Add support for interrupt polarity defined in device tree

The da9062 interrupt handler cannot necessarily be low active.
Add a function to configure the interrupt type based on what is defined in the device tree.
The allowable interrupt type is either low or high level trigger.

Signed-off-by: Shreyas Joshi <shreyas.joshi@biamp.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>