Support keyboard typematic.

Mainly add a typematic task that counts down the delay. Set the initial delay
in the keyboard_state_changed() when key pressed and clean it when released.

BUS=chrome-os-partner:8463
TEST=press on a particular key and screen shows that key is repeating.

Change-Id: Ic8432f8b38b514476588e0b7ad8fdc8a0b0c0b51
3 files changed