wifi: rtw89: 8922a: add set_channel MAC part

To set channel, add a function to get TXSB (TX subband) that is hardware
index to indicate primary channel. Then, configure band, channel,
bandwidth and TXSB via registers.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20240215055741.14148-2-pkshih@realtek.com