Allow getattr on tempfs files

This is needed by linker to be able to load libraries from memfd
which currently generated following denial:
avc: denied { getattr } for path=2F6D656D66643A666F6F626172202864656C6574656429 dev="tmpfs" ino=902079 scontext=u:r:shell:s0 tcontext=u:object_r:shell_tmpfs:s0 tclass=file permissive=0

Bug: http://b/37245203
Bug: http://b/37916741
Test: builds
Change-Id: I5b57b6cada50a62657c8daaaaaa56f1ee9cdb376