Input: omap-keypad - set up irq type from DT

OMAP4 is DT only, so read the keypad IRQ type from DT instead hard-coding
it in the driver.

Signed-off-by: Illia Smyrnov <illia.smyrnov@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>