Input: ff-memless - add notion of direction to for rumble effects

This adds simple direction calculation when combining effects. It's useful
to decide motor direction for rumble (vibrator).

Signed-off-by: Jari Vanhala <ext-jari.vanhala@nokia.com>
Acked-by: Anssi Hannula <anssi.hannula@iki.fi>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>