Change TV strings to work across form-factors

Android TV devices come in a variety of form factors.
Besides panel TV devices, it also runs on set top boxes, HDMI dongles,
soundbars, etc. Some strings referred to the ATV device as "TV", which
might be confusing to a user who sees the TV as his panel TV devices
that the ATV device is only connected to.
This change makes the wording of those strings more generic, so that
they fit for any ATV form-factor.

Bug: 138633871
Test: build
Change-Id: I7517a6b6064deb53718622bca39e43b320349abc