Input: edt-ft5x06 - do not hardcode interrupt trigger type

Instead of hardcoding IRQ trigger type to IRQF_TRIGGER_FALLING, let's
respect settings specified in device tree. To be compatible with older
DTSes, if trigger type is not set up in DTS we'll set it to default
(falling edge).

Tested-by: Franklin S Cooper Jr <fcooper@ti.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>