allow system_server block_suspend

I'm only seeing this denial on one device (manta), but it feels like
it should be part of the generic policy. I don't understand
why it's happening on only one device.

Addresses the following denial:

14.711671   type=1400 audit(1387474628.570:6): avc:  denied  { block_suspend } for  pid=533 comm="InputReader" capability=36  scontext=u:r:system_server:s0 tcontext=u:r:system_server:s0 tclass=capability2

Change-Id: If4b28b6f42ca92c0e2cacfad75c8cbe023b0fa47

system_server.te

@@ -37,6 +37,8 @@ allow system_server self:capability {
     sys_tty_config
 };
 
+allow system_server self:capability2 block_suspend;
+
 # Triggered by /proc/pid accesses, not allowed.
 dontaudit system_server self:capability sys_ptrace;