rsi: update set_channel command frame

TX command frame set_channel is modified to use common
descriptor structure. Also DFS channel indication to firmware
is added in the descriptor for dfs channels configuration.

Signed-off-by: Prameela Rani Garnepudi <prameela.j04cs@gmail.com>
Signed-off-by: Amitkumar Karwar <amit.karwar@redpinesignals.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>