WPS: Add UFD support (USBA out-of-band mechanism)

WPS: Add UFD support (USBA out-of-band mechanism)

This patch is only for the following use case:
- Enrollee = wpa_supplicant
- Registrar = hostapd internal Registrar

Following UFD methods can be used:
- Enrollee PIN with UFD
- Registrar PIN with UFD
- unencrypted credential with UFD

Encrypted credentials are not supported.

Enrollee side operation:
wpa_cli -i ath0 wps_oob <device type> <mount point> <oob method>
    oob method = pin-e/pin-r/cred

wpa_cli -i ath0 wps_oob ufd /mnt/ pin-r

Registrar side operation:
./hostapd_cli -i ath0 wps_oob <device type> <mount point> <oob method>
    oob method = pin-e/pin-r/cred

hostapd_cli -i ath0 wps_oob ufd /mnt/ cred