Input: omap-keypad - convert to threaded IRQ

Convert to use threaded IRQ.

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>