Usb: Add property for multi usb mode.

Property for multi usb mode is used by UsbAlsaManager to decide if only
one or multiple USB devices can be connected to audio system at a
certain time.

Bug: 262415494
Test: TH
Change-Id: I9481883fa8977329d35b139713aad15e995306b1
diff --git a/private/property_contexts b/private/property_contexts
index 603c70b..a2d7d14 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -390,6 +390,10 @@
 # to enable head tracking for spatial audio
 ro.audio.headtracking_enabled u:object_r:audio_config_prop:s0 exact bool
 
+# Boolean property used in UsbAlsaManager to decide if only one or multiple
+# USB devices can be connected to audio system at a certain time
+ro.audio.multi_usb_mode u:object_r:audio_config_prop:s0 exact bool
+
 persist.config.calibration_fac u:object_r:camera_calibration_prop:s0 exact string
 
 config.disable_cameraservice u:object_r:camera_config_prop:s0 exact bool