add line out to device sharing codec backend

AUDIO_DEVICE_OUT_LINE was not listed in
AUDIO_DEVICE_OUT_ALL_CODEC_BACKEND causing a loss of audio when
music was playing over line out and a ringtone playing over lineout and speaker
was stoppped.

Bug: 18903885.
Change-Id: I8c132db9cbfb17842a463600a2d0ced214244b72