rsi: Add support for 802.11d

Transmit power level in a channel is determined based on the dfs region.
To support regulatory rules dfs region should be configured to device during
set channel request. Also antenna gain values are taken from the mac80211
channel parameters instead of fixed values.

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