Allow /dev/goldfish_sync

manual cherry pick of:
https://googleplex-android-review.git.corp.google.com/#/c/1024926/

Change-Id: I41883eafd2b261d000c41eaf3ba04af7e2b89349
(cherry picked from commit 10bbf13fe7a3c2bfa28a4f560bb6f85de4edf786)
diff --git a/target/board/generic/sepolicy/file_contexts b/target/board/generic/sepolicy/file_contexts
index e8d32f7..e9502d9 100644
--- a/target/board/generic/sepolicy/file_contexts
+++ b/target/board/generic/sepolicy/file_contexts
@@ -9,6 +9,7 @@
 /dev/block/vdc               u:object_r:userdata_block_device:s0
 
 /dev/goldfish_pipe           u:object_r:qemu_device:s0
+/dev/goldfish_sync           u:object_r:qemu_device:s0
 /dev/qemu_.*                 u:object_r:qemu_device:s0
 /dev/socket/qemud            u:object_r:qemud_socket:s0
 /dev/ttyGF[0-9]*             u:object_r:serial_device:s0