audio policy: do not consider telephony TX device as a local device

Exclude playback over AUDIO_DEVICE_OUT_TELEPHONY_TX when evaluating
local playback activity on a HW module as this is a virtual device
injecting audio to telephony TX path and as such not interfering
with local playback.

Bug: 159480161
Test: repro steps in bug
Change-Id: I8cd27acc0033725fa66f95c7661c58b38d31532a