ucm2: Qualcomm: Radxa Dragon Q6A: keep the headphone route when using HDMI

[GitHub pull_request - opened <github@alsa-project.org>]

alsa-project/alsa-ucm-conf pull request #906 was opened from MarcHT91:

MultiMedia1 (hw:0) feeds the headphones and MultiMedia2 (hw:1) feeds
DisplayPort/HDMI. Each AudioReach back end accepts a single front end, so
connecting MultiMedia2 to RX_CODEC_DMA_RX_0 disconnects MultiMedia1.

The HiFi verb did exactly that ('RX_CODEC_DMA_RX_0 Audio Mixer
MultiMedia2' = 1), and the HDMI device then wrote 0 to the same control,
which on current kernels also clears the back end's link. After

  alsaucm -c hw:0 set _verb HiFi set _enadev HDMI

the headphones are disconnected, and a stream started on hw:0 never
advances (hw_ptr stays at 0):

  before: RX<-MM1=on   RX<-MM2=off  DP<-MM2=on
  after:  RX<-MM1=off  RX<-MM2=off  DP<-MM2=on

Keep each front end on its own back end: the verb clears the unused
routes and connects MultiMedia1 to the headphones, and the HDMI device
only switches 'DISPLAY_PORT_RX_0 Audio Mixer MultiMedia2'. The zero
writes come before the connections, so the order is also safe on kernels
where writing 0 to a route control drops whatever link the back end has
(fix sent to ASoC: "ASoC: qcom: audioreach: only disconnect the route a
mixer control owns").

Tested on a Radxa Dragon Q6A: verb only, verb + HDMI, verb + Headphones
+ HDMI, HDMI enable/disable: the headphone route stays connected in all
cases.

Fixes: 67628fb4871e ("ucm2: Qualcomm: add Radxa Dragon Q6A")

Request URL   : https://github.com/alsa-project/alsa-ucm-conf/pull/906
Patch URL     : https://github.com/alsa-project/alsa-ucm-conf/pull/906.patch
Repository URL: https://github.com/alsa-project/alsa-ucm-conf