mwifiex: separate interface combination for multichannel and DFS

Multichannel and DFS cannot be supported at same time. So when multichannel
operation is enabled by module parameter, we enable number of channel as 2
while registering wiphy. For all other cases we advertise DFS support to
cfg80211. Patch also adds support for radar detect widths parameter.

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>