Add a notification when console is active

Performance is largely impacted when console is running, and device
should not ship with that configuration. Moreover, we have seen cases,
when performance of new features was tested with UART on. This CL adds a
notification when console service is active indicating UART is on.

Fixes: 119623211
Test: Enable UART and see warning after boot
Test: Disable UART and no warning
Change-Id: Ie60f763088a15608027986ac855466eb7fc97264