Sepolicy: Add policy rules for untrusted_app context

Add gpu related policy rules for untrusted_app

Addressing the following denial:

type=1400 audit(0.0:593): avc: denied { search } for name="gpu" dev="dm-0"
ino=405 scontext=u:r:untrusted_app:s0:c144,c256,c512,c768
tcontext=u:object_r:vendor_gles_data_file:s0 tclass=dir permissive=0
app=com.android.chrome

Change-Id: Iabbc7bea6f00a055f7f0ea3d2b926225737b99d5