Implement hotplug detection sequence.

Hotplug detection is periodic operation to detect new/removed device.
In case of directly connected device fires hotplug devices
but remote devices which are plugged in hdmi switch may not
report their existence.
Hotplug action polls all devices in regular base; 5s for
system audio (only when it's active) 15s for others.

Change-Id: I77c308ecfd5d6bf92f306923fa5ac9eabdad4127