wifi: rtw89: 8851b: add set channel function

Set MAC/BB/RF registers according to channel we are going to set. In
additional, certain channels or bands need more deals, such as enable CCK
in 2 GHz band, spur elimination at certain frequencies.

The set channel helper is used to save/restore states before/after setting
channel, and does reset BB to prevent hardware getting stuck in abnormal
state during switching channel and receiving data.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230512061220.16544-6-pkshih@realtek.com