Label /dev/hvcN paths

They are virtual console devices. Label them as serial_devices.

Bug: 200914564
Test: m
Change-Id: I6a178360fa9977e9b50b0c07da2a506114369189
diff --git a/microdroid/system/private/file_contexts b/microdroid/system/private/file_contexts
index e28f4fc..89fa02f 100644
--- a/microdroid/system/private/file_contexts
+++ b/microdroid/system/private/file_contexts
@@ -82,6 +82,7 @@
 /dev/uinput		u:object_r:uhid_device:s0
 /dev/uio[0-9]*		u:object_r:uio_device:s0
 /dev/urandom		u:object_r:random_device:s0
+/dev/hvc0		u:object_r:serial_device:s0
 /dev/vhost-vsock	u:object_r:kvm_device:s0
 /dev/vndbinder		u:object_r:vndbinder_device:s0
 /dev/vsock		u:object_r:vsock_device:s0