brcmfmac: use struct brcmf_if as interface object for fwil functions

The functions for communicating were given the net_device only because
its private data contained struct brcmf_if object. However, not all
firmware related interfaces will be associated with a net_device. To
accomodate provisioning firmware for such interfaces the struct
brcmf_if object will be passed to the fwil functions.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>