input: Hack for trackball wake.

The action button is now considered a Motion event only, and not
passed through the same path as key events, so it isn't subject to
the normal interception keys are subject to.

The proper solution is probably to add a method for the policy to
intercept the correct event, instead of creating another one as I
am doing here.  However, it should probably only be called for
button presses (AMOTION_EVENT_ACTION_DOWN/UP), since movements are
fairly frequent when they're happening.

This patch simply generates a fake key event (BTN_MOUSE) for
button presses that are processed and then dropped by the phone
policy.  This patch may add latency to trackpad presses, but they
are not likely to be significant for normal use.

Change-Id: If0cd8b0ead3bf5574303c2804216690301340a3e