wifi: rtw89: coex: Add Bluetooth RSSI level information

In order to control RF LNA setting, need Bluetooth RSSI level information.
RSSI level separate Bluetooth RSSI to several level, so the mechanism can
assign a corresponding setting.

Signed-off-by: Ching-Te Ku <ku920601@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20231218061341.51255-9-pkshih@realtek.com