28 mapping workaround for devices upgrading to P.

Bug: 72458734
Test: Compile current system sepolicy with P vendor sepolicy
Test: Plug in a P device then do:
m selinux_policy
cp $OUT/system/etc/selinux/plat_sepolicy.cil  plat_sepolicy.cil
cp $ANDROID_BUILD_TOP/system/sepolicy/private/compat/28.0/28.0.cil 28.0.cil
adb pull /vendor/etc/selinux/plat_pub_versioned.cil
adb pull /vendor/etc/selinux/vendor_sepolicy.cil
secilc plat_sepolicy.cil -m -M true -G -N -c 30 28.0.cil \
plat_pub_versioned.cil vendor_sepolicy.cil
Change-Id: I399b3a204eb94bee0ba1b5024b1c3463219c678e

private/compat/28.0/28.0.cil

@@ -11,6 +11,9 @@
 (expandtypeattribute (vold_socket_28_0) true)
 (typeattributeset vold_socket_28_0 (vold_socket))
 
+;; TODO b/111680480: remove once we have consistent P sepolicy on all devices.
+(typeattribute exported_audio_prop_28_0)
+
 (expandtypeattribute (accessibility_service_28_0) true)
 (expandtypeattribute (account_service_28_0) true)
 (expandtypeattribute (activity_service_28_0) true)