exclude su from app auditallow

su is an appdomain, and as such, any auditallow statements applicable to
appdomain also apply to su. However, su is never enforced, so generating
SELinux denials for such domains is pointless. Exclude su from
ion_device auditallow rules.

Addresses the following auditallow spam:

  avc: granted { ioctl } for comm="screencap" path="/dev/ion" dev="tmpfs"
  ino=10230 ioctlcmd=4906 scontext=u:r:su:s0
  tcontext=u:object_r:ion_device:s0 tclass=chr_file

Test: policy compiles
Change-Id: I2e783624b9e53ad365669bd6f2d4db40da475a16

public/app.te

@@ -239,9 +239,9 @@ allowxperm { appdomain -bluetooth } self:{ rawip_socket tcp_socket udp_socket }
 
 allow { appdomain -isolated_app } ion_device:chr_file rw_file_perms;
 # TODO is write really necessary ?
-auditallow appdomain ion_device:chr_file { write append };
+auditallow { appdomain userdebug_or_eng(`-su') } ion_device:chr_file { write append };
 # TODO audit ion ioctl usage by apps
-auditallow appdomain ion_device:chr_file ioctl;
+auditallow { appdomain userdebug_or_eng(`-su') } ion_device:chr_file ioctl;
 
 allow { appdomain -isolated_app } hal_graphics_allocator:fd use;