CEC: Generate hotplug events upon adding listener

CEC HAL does not report initial connection state of the HDMI port
but does it only when the state is updated. For the listeners which
want to get the initial state of the ports, this CL generates
hotplug event per each port when a new listener is added.

Bug: 18488079

Change-Id: I6915a96e3c14ee0db1bfb6912ab77d3ea1bd2f07