alsa-profiles: use SB Audigy PCM mixer controls

Creative Labs Sound Blaster Audigy cards (snd_emu10k1 driver) expose
mixer controls named 'PCM Front', 'PCM Rear', etc. in addition to the
more common 'Front', 'Rear', etc.  The latter seem to be intended for
a stereo-to-all-speakers mirroring mode that we do not use, and have
no effect when we adjust them.
https://docs.kernel.org/sound/cards/audigy-mixer.html

We therefore define a custom mixer path for Audigy devices, using the
PCM mixer controls.

This has been tested on an Audigy 5/Rx.  Based on a brief look at the
ALSA driver, I think all Audigy devices (vendor 0x1102, device 0x0004
or 0x0008) have the same PCM controls, making this change probably safe
for our existing Audigy udev rules.

Relevant kernel files:
sound/pci/emu10k1/emu10k1_main.c
sound/pci/emu10k1/emufx.c
include/sound/emu10k1.h

Fixes #2934

spa/plugins/alsa/mixer/paths/analog-output-audigy.conf

@@ -0,0 +1,55 @@
+; Mixer path for the Sound Blaster Audigy series, which uses the EMU10K2 DSP.
+; We target 'PCM Front' and similarly named controls instead of 'Front' et al.
+; because the latter have no effect on volume, apparently intended for a
+; stereo-to-all-speakers mirroring mode that we do not use.
+; https://docs.kernel.org/sound/cards/audigy-mixer.html
+;
+; See analog-output.conf.common for an explanation on the directives
+
+[General]
+priority = 99
+description-key = analog-output
+
+[Element Master]
+switch = mute
+volume = merge
+override-map.1 = all
+override-map.2 = all-left,all-right
+
+[Element PCM Front]
+switch = mute
+volume = merge
+override-map.1 = all-front
+override-map.2 = front-left,front-right
+
+[Element PCM Rear]
+switch = mute
+volume = merge
+override-map.1 = all-rear
+override-map.2 = rear-left,rear-right
+
+[Element PCM Surround]
+switch = mute
+volume = merge
+override-map.1 = all-rear
+override-map.2 = rear-left,rear-right
+
+[Element PCM Side]
+switch = mute
+volume = merge
+override-map.1 = all-side
+override-map.2 = side-left,side-right
+
+[Element PCM Center]
+switch = mute
+volume = merge
+override-map.1 = all-center
+override-map.2 = all-center,all-center
+
+[Element PCM LFE]
+switch = mute
+volume = merge
+override-map.1 = lfe
+override-map.2 = lfe,lfe
+
+.include analog-output.conf.common