emulator: fix widevine drm vndbinder denial

[   86.252399] type=1400 audit(1503684692.153:25): avc: denied { read write } for pid=4160 comm="android.hardwar" name="vndbinder" dev="tmpfs" ino=5163 scontext=u:r:hal_drm_widevine:s0 tcontext=u:object_r:vndbinder_device:s0 tclass=chr_file permissive=0

BUG: 64726466

Test: build sdk_gphone_x86-user target, launch it
and the above denial should be fixed.

Change-Id: Ied1268878236c42fbb0751a0f33014b332d78c32