Input: tca8418 - use the interrupt trigger from the device tree

The TCA8418 might be used using different interrupt triggers on various
boards. This is not working so far because the current code forces a
falling edge trigger.

The device tree already provides a trigger type, so let's use whatever it
sets up, and since we can be loaded without DT, keep the old behaviour for
the non-DT case.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>