wifi: rtw89: add RSSI based antenna diversity

wifi: rtw89: add RSSI based antenna diversity

RSSI statistics are grouped by CCK, OFDM or non-legacy rate. These
statistics will be collected in training state for both (main/aux)
antenna. There is a time period (ANTDIV_DELAY) for rate adaptive
settle down before start collect statistics when switch antenna.

Antenna diversity checks packet count from training state for each
group and use the most one as the final RSSI for comparison, and
then choose the better one as target antenna.

Signed-off-by: Eric Huang <echuang@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/20230418012820.5139-7-pkshih@realtek.com