sepolicy: allow vold to mount ext4 sdcard

* Originally in 9a19f575a4c991bf2d7bc2f8f980909910ee4cce vendor/cm

Change-Id: I58e28fff82b681940d2ab9c1681727324d6503cd
WFD : Adding policy exceptions in app domain for wfd

This is change is to allow wfd_app domain some exceptions
which are not allowed for entities generally derived from
app domain. This is required as the app domain policies
are in conflict with the wfd_app domain policies

Change-Id: I26536d083fb5615cffef81d10260cb6704dc8955