ath10k: enable the BT-coex feature

The new 10.2.4 FW support the BT-coex feature with external BT module,
The external BT modules can communicate with it via the GPIO. This patch
check the BT-coex capability of the FW and enable it by default.

Signed-off-by: Yanbo Li <yanbol@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>