Input: cros_ec_keyb: Stop handling interrupts directly

Because events other that keyboard ones will be handled by now on by
other drivers, stop directly handling interrupts and instead listen to
the new notifier in the MFD driver.

Signed-off-by: Vic Yang <victoryang@google.com>
Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>