wifi: rtw89: 8922a: update the register used in DIG and the DIG flow

DIG standing for dynamic initial gain that is used to adjust RX coverage,
and PD lower threshold is packet detection power level by received signal
strength to avoid false detection of the WiFi packet.

Because of the hardware is different between WiFi 7 and 6 ICs, we adjust
flow and add register definition for 8922A.

Signed-off-by: Cheng-Chieh Hsieh <cj.hsieh@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20240105064228.36580-5-pkshih@realtek.com