Mark vr_wm as coredomain

This couldn't be done in earlier because this domain does not yet exist
in AOSP master.

Test: mmm system/sepolicy -- no errors
Bug: 35870313
Change-Id: I323e5c22e471cd1900b88d0d1d4edfb5973a33d7

private/vr_wm.te

 # vr_wm - VR Window Manager
+typeattribute vr_wm coredomain;
 
 # The vr_wm is started by init.
 init_daemon_domain(vr_wm)