CEC: Handles initiation of press-and-hold correctly

Previously the time gap between the first and the second key event
for repeated keys(press-and-hold) can be bigger than the threshold,
which violates CEC spec. This CL rectifies it by managing its own
state rather than relying on Android key handler.

Bug: 19117830

Change-Id: Iedfa48f9ab826252e8616d1c3b7491e8b8333c81