drmserver: allow looking in efs_file directories

We can read any efs_files, but can't look in the directory
containing them. Allow it.

Without this patch, high resolution movie playback is broken.

Addresses the following denial:

[  276.780046] type=1400 audit(1391105234.431:5): avc:  denied  { search } for  pid=125 comm="drmserver" name="/" dev="mmcblk0p1" ino=2 scontext=u:r:drmserver:s0 tcontext=u:object_r:efs_file:s0 tclass=dir

Bug: 12819852

Change-Id: Ie9d13a224cef5e229de1bdb78d605841ed387a21