alsa-mixer: add support for Sennheiser GSX 1000 gaming DAC

This same profile should also work for the GSX 1200, but I don't know the USB id
for that.

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/257>

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

@@ -0,0 +1,5 @@
+; Some gaming devices have a separate "chat" device, this is for voice chat
+; while playing games. This device is just a fairly standard analog mono
+; device, but it's nicer to make it clear that this is the "chat" device
+; as is mentioned in the marketing info and manual.
+.include analog-output.conf.common

src/modules/alsa/mixer/paths/virtual-surround-7.1.conf

@@ -0,0 +1,5 @@
+[Element PCM,1]
+switch = mute
+volume = merge
+override-map.1 = all
+override-map.2 = all-left,all-right

src/modules/alsa/mixer/profile-sets/sennheiser-gsx.conf

@@ -0,0 +1,58 @@
+# This file is part of PulseAudio.
+#
+# PulseAudio is free software; you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as
+# published by the Free Software Foundation; either version 2.1 of the
+# License, or (at your option) any later version.
+#
+# PulseAudio is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.
+
+; USB Gaming DAC.
+; These devices have two output devices. The first one is mono, meant for
+; voice audio, and the second one is 7.1 surround, meant for everything
+; else. The 7.1 surround is mapped to headphones within the device.
+; The purpose of the mono/7.1 design is to provide separate volume
+; controls for voice and other audio, which can be useful in gaming.
+;
+; Works with:
+; Sennheiser GSX 1000
+; Sennheiser GSX 1200
+;
+; See default.conf for an explanation on the directives used here.
+
+[General]
+auto-profiles = no
+
+[Mapping analog-chat-output]
+device-strings = hw:%f,0
+channel-map = mono
+paths-output = analog-chat-output
+direction = output
+priority = 4000
+intended-roles = phone
+
+[Mapping analog-output-surround71]
+device-strings = hw:%f,1
+channel-map = front-left,front-right,rear-left,rear-right,front-center,lfe,side-left,side-right
+paths-output = virtual-surround-7.1
+priority = 4100
+direction = output
+
+[Mapping analog-chat-input]
+device-strings = hw:%f,0
+channel-map = mono
+paths-input = analog-chat-input
+priority = 4100
+direction = input
+
+[Profile output:analog-output-surround71+output:analog-output-chat+input:analog-input]
+output-mappings = analog-output-surround71 analog-chat-output
+input-mappings = analog-chat-input
+priority = 5100
+skip-probe = yes