Hello Hiroyuki Hara,
The i.MX6 SABRE board do not have a Wifi Module, but there are several alternatives. One of the most popular is using a Wifi module trough the SDIO interface. You would need to obtain the driver from the Wifi module manufacturer.
The Android 7.1 BSP does has support for the Broadcom BCM4339 SDIO Card (Murata TypeZP Ver2.0 SDIO module as it’s used by the WiFi Display Sink Feature. You may look for more information on the BSP Release Notes.
Other module that you may use is Silex’s. They have an application note that shows how to integrate their SD-SDCAN Wifi Module on the i.MX6 SABRE (link below).
https://community.nxp.com/docs/DOC-100670
I hope this information helps!
Regards,