Add rules for vfat for sdcardfs

This adds parellel rules to the ones added for media_rw_data_file
to allow apps to access vfat under sdcardfs. This should be reverted
if sdcardfs is modified to alter the secontext it used for access to
the lower filesystem

Change-Id: Idb123206ed2fac3ead88b0c1ed0b66952597ac65
Bug: 62584229
Test: Run android.appsecurity.cts.ExternalStorageHostTest with
      an external card formated as vfat
Signed-off-by: Daniel Rosenberg <drosen@google.com>