rtw89: include subband type in channel params

Make stuffs related to channel be collected in channel_params,
and encapsulate the corresponding decision in get_channel_params().
Then, functions that takes channel_params can also notice subband type.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220113011042.6705-2-pkshih@realtek.com