Add permission for VFIO device binding

vfio_handler will bind platform devices to VFIO driver, and then
return a file descriptor containing DTBO. This change adds
permissions needed for that.

Bug: 278008182
Test: adb shell /apex/com.android.virt/bin/vm run-microdroid \
      --devices /sys/bus/platform/devices/16d00000.eh --protected
Change-Id: Ie947adff00d138426d4703cbb8e7a8cd429c2272
diff --git a/apex/com.android.virt-file_contexts b/apex/com.android.virt-file_contexts
index 9c13bd5..afe9f51 100644
--- a/apex/com.android.virt-file_contexts
+++ b/apex/com.android.virt-file_contexts
@@ -3,3 +3,4 @@
 /bin/fd_server             u:object_r:fd_server_exec:s0
 /bin/virtmgr               u:object_r:virtualizationmanager_exec:s0
 /bin/virtualizationservice u:object_r:virtualizationservice_exec:s0
+/bin/vfio_handler          u:object_r:vfio_handler_exec:s0