selftests: memfd: add config fragment for fuse

The memfd test requires to insert the fuse module (CONFIG_FUSE_FS).
Signed-off-by: NAnders Roxell <anders.roxell@linaro.org>
Signed-off-by: NDaniel Díaz <daniel.diaz@linaro.org>
Signed-off-by: NShuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/memfd/config

+CONFIG_FUSE_FS=m