CEC: Use isConnected() to check ARC transmission feasibility

Whenever every hotplug event occurs, ARC feature has been
disabled/enabled if needed in order not to establish ARC connection if
+5V status is false. The check, whether feature should be
disabled/enabled or not, is based on the device info of AVR. But it may
malfunction if the device info is stale because of rapid and repeated
plug in/out. This change simplifies this check by using isConnected()
instead of disabling/enabling full ARC feature.

Bug: 33567002
Test: Applied this change and plug in/out rapidly on archer.
Change-Id: I420270193d2f60f61f3c39a151c7e06d326651d2
(cherry picked from commit b0fd6a1bed5d522673233fbd51d1d7508c790c0c)