feat: audio stack working — pulseaudio + x6200_control + voice_rec

- Add pulseaudio in system mode
- Add alsactl restore with correct mixer state from Aether
- Add x6200-control package (I2C hardware control library)
- Audio chain: pulseaudio -> x6200_control_init -> voice_rec -> speaker

br2_external/board/x6200/rootfs-overlay/etc/asound.conf

@@ -0,0 +1,88 @@
+# direct mix for pcm playback
+# aplay -D mixplayback xxx.wav
+pcm.mixout {
+	type dmix
+	ipc_key 1024
+	slave {
+		# slave PCM name
+		pcm "hw:0,0"
+
+		# PCM params
+		format       S16_LE # STR
+		rate         16000  # INT
+		#rate         48000  # INT
+		channels     2      # INT
+
+		# stream params,buffer_size=period x period_size
+		periods      100   # INT,when buffer_size or buffer_time is not specified
+		period_size  1024   # INT,in frames,3 times than app need
+
+		# optional params
+		# period_time  0    # INT,in usec
+		# buffer_time  0    # INT,in usec
+		# buffer_size  65536  #INT,in frames
+	}
+	bindings {
+		0 0 # from 0 -> 0
+		1 1 # from 1 -> 1
+	}
+	# slowptr BOOL # slow but more precise pointer updates
+}
+
+# dsnoop for capture
+# arecord -D mixcapture test.wav
+pcm.mixin {
+	type dsnoop
+	ipc_key 1025 # must be unique for all dmix plugins!!!!
+	# ipc_key_add_uid yes # no need for embedded system
+	slave {
+		# slave PCM name
+		pcm "hw:0,0"
+
+		# PCM params
+		format       S16_LE # STR
+		rate         16000  # INT
+		#rate         48000  # INT
+		channels     2      # INT
+
+		# stream params,buffer_size=period x period_size
+		periods      100   # INT,when buffer_size or buffer_time is not specified
+		period_size  1024   # INT,in frames,3 times than app need
+
+		# optional params
+		# period_time  0    # INT,in usec
+		# buffer_time  0    # INT,in usec
+		# buffer_size  65536  #INT,in frames
+	}
+	bindings {
+		0 0 # from 0 -> 0
+		1 1 # from 1 -> 1
+	}
+ }
+
+# pcm plug for playback
+pcm.mixplayback {
+	type plug
+	slave.pcm "mixout"
+	# A hint is required for listing the device in some GUIs
+	hint {
+		show on
+		description "X6200 playback mixer"
+	}
+}
+
+# pcm plug for capture
+pcm.mixcapture {
+	type plug
+	slave.pcm "mixin"
+	# A hint is required for listing the device in some GUIs
+	hint {
+		show on
+		description "X6200 capture mixer"
+	}
+}
+
+ctl.mixer0 {
+	type hw
+	card 0
+}