brcmfmac: Enable 40MHz bandwidth in 2GHz band and OBSS scanning operations

This patch enables 40MHz bandwidth in 2GHz band after checking whether
cfg80211 allows it or not, and enables OBSS scanning operations to
to support 20/40 BSS coexistence.

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