selinux: Downgrade CMFM's domain

the filemanager doesn't need to be in platform_app. Put it in untrusted_app,
especially since it's a possible su client

Change-Id: I164853f2c8721d86b5b90677cb33032a3b491ff5
Merge branch 'cm-12.0' of git://github.com/CyanogenMod/android_vendor_cm into cm-12.0