mwifiex: support to set multichannel policy to FW

This patch adds support for setting multichannel policy as module parameter
to FW. Value of 1 indicates Multichannel support is enabled
and value of 0 disables it.

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