Hello sumo,
It is very necessary to add wifi to device tree, for example:
(1) Multiplexing SDIO PINs connected to WIFI card
(2) Initializing corresponding data structure of SDIO
(3) Initializing GPIOs for controlling WIFI's power and reset.
...
Above work must be done in BSP.
Hope above advice can help you !
Regards,
Weidong