palm_cover: separate palm_cover BEGIN and END events sending

palm_cover: separate palm_cover BEGIN and END events sending

Before, the palm_cover event was regarded as a momentary gesture rather than
a continuous one.

Current:
event's axis value is 1, both the palm_cover BEGIN and END events are sent.
event's axis value is 0, no palm_cover event is sent.

Modified:
event's axis value is 1, palm_cover BEGIN event is sent.
event's axis value is 0, palm_cover END event is set.

(FYI, How palm_cover gesture is generated:
ABS_MT_PALM value --> libinput touch event's aux data
--> E20 ecore_event_add(ECORE_EVENT_AXIS_UPDATE,
--> e-mod-tizen-gesture sends palm_cover event using tizen_gesture protocol)

Change-Id: If08bc917f9faa069397fd34ae6bc3faa84623f6c