ucm2: PinePhone: use "Mix Mono" routing for earpiece

alsa-project/alsa-ucm-conf pull request #324 was opened from a-wai:

The earpiece speaker is a mono device, using only a single channel (in our case, the left one) from the DA0 output. This causes loss of information as the right channel is completely discarded when playing stereo audio.

In order to avoid this issue, set `AIF1 DA0 Stereo Playback Route` to `Mix Mono` when using the "Earpiece" output port (and only in this case).

Request URL : https://github.com/alsa-project/alsa-ucm-conf/pull/324 Patch URL : https://github.com/alsa-project/alsa-ucm-conf/pull/324.patch Repository URL: https://github.com/alsa-project/alsa-ucm-conf