mel: add vfat to minnow MACHINE_FEATURES

Minnow has USB host, so we need vfat support for USB storage.

JIRA: SB-3161

Signed-off-by: Christopher Larson <kergoth@gmail.com>
Merge pull request #253 from kergoth/sb-3161

mel: add vfat to minnow MACHINE_FEATURES