Allow boot animation to update boot status.

This CL was missed from the topic:
https://android-review.googlesource.com/q/topic:bootanim-percent

Test: update ART module, see animation go to 100%
Bug: 184881321
Change-Id: I59706718af11751a7e1f4b5ab1ff2793f554fb19
diff --git a/private/bootanim.te b/private/bootanim.te
index cc6e0db..855bc3d 100644
--- a/private/bootanim.te
+++ b/private/bootanim.te
@@ -11,4 +11,7 @@
 # Read ro.boot.bootreason b/30654343
 get_prop(bootanim, bootloader_boot_reason_prop)
 
-get_prop(bootanim, bootanim_config_prop)
\ No newline at end of file
+get_prop(bootanim, bootanim_config_prop)
+
+# Allow updating boot animation status.
+set_prop(bootanim, bootanim_system_prop)