alsa-mixer: Add possibility to configure ELD device

The alsa mixer kcontrol has "device index" 3, 7, 8, and 9.
We need to configure this properly.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>

src/modules/alsa/mixer/paths/analog-output.conf.common

@@ -59,6 +59,8 @@
 ; mute-during-activation = yes | no      # If this path supports hardware mute, should the hw mute be used while activating this
 ;                                        # path? In some cases this can reduce extra noises during port switching, while in other
 ;                                        # cases this can increase such noises. Default: no.
+; eld-device = ...                       # If this is an HDMI port, here's where to specify the device number for the ELD mixer
+;                                        # control. The default is to not make use of ELD information.
 ;
 ; [Properties]                           # Property list for this path. The list is merged into the port property list.
 ; <key> = <value>                        # Each property is defined on its own line.

src/modules/alsa/mixer/paths/hdmi-output-0.conf

@@ -1,6 +1,7 @@
 [General]
 description = HDMI / DisplayPort
 priority = 59
+eld-device = 3
 
 [Properties]
 device.icon_name = video-display

src/modules/alsa/mixer/paths/hdmi-output-1.conf

@@ -1,6 +1,7 @@
 [General]
 description = HDMI / DisplayPort 2
 priority = 58
+eld-device = 7
 
 [Properties]
 device.icon_name = video-display

src/modules/alsa/mixer/paths/hdmi-output-2.conf

@@ -1,6 +1,7 @@
 [General]
 description = HDMI / DisplayPort 3
 priority = 57
+eld-device = 8
 
 [Properties]
 device.icon_name = video-display

src/modules/alsa/mixer/paths/hdmi-output-3.conf

@@ -1,6 +1,7 @@
 [General]
 description = HDMI / DisplayPort 4
 priority = 56
+eld-device = 9
 
 [Properties]
 device.icon_name = video-display