brcmfmac: rework wiphy structure setup

Instead of waiting for IFF_UP of the primary net device to determine
the band and channel information of the wiphy structure, this is now
done during driver initialization in brcmf_cfg80211_attach(). The
channel information is obtained from the device and the 2G band is
updated when 40MHz bandwidth is enabled for that band. Before this
change the band and channel objects were common between multiple
brcmfmac devices in the system, which make that information rather
unreliable. That is also fixed with this reworked implementation.
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>