allow system_server to set bootanim scheduling priority

Addresses the following denial:
     avc: denied { setsched } for pid=1405 comm="Binder:1094_3" scontext=u:r:system_server:s0 tcontext=u:r:bootanim:s0 tclass=process permissive=0

Maybe fix bug 30118894.

Bug: 30118894
Change-Id: I29be26c68094c253778edc8e4fef2ef1a238ee2e

system_server.te

@@ -89,6 +89,7 @@ allow system_server { appdomain autoplay_app }:process { getsched setsched };
 allow system_server audioserver:process { getsched setsched };
 allow system_server cameraserver:process { getsched setsched };
 allow system_server mediaserver:process { getsched setsched };
+allow system_server bootanim:process { getsched setsched };
 
 # Read /proc/pid data for all domains. This is used by ProcessCpuTracker
 # within system_server to keep track of memory and CPU usage for