rtw88: coex: fix A2DP stutters while WL busy + WL scan

While WL scan, WL is more high priority than BT. The packets from AP
will be a big interference to A2DP. It will lead to A2DP stutters. Stop
answering CTS to AP to decrease AP's packets Tx while WL scan + WL busy.
Enable BT AFH feature to make BT leave away from WL channel.

Desired BT firmware BT-COEX version: 0x1c
Desired WL firmware version: 9.9.x

Signed-off-by: Ching-Te Ku <ku920601@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210319054218.3319-8-pkshih@realtek.com