ath10k: disable wake_tx_queue for older devices

Ideally wake_tx_queue should be used regardless as
it is a requirement for reducing bufferbloat and
implementing airtime fairness in the future.

However some setups (typically low-end platforms
hosting QCA988X) suffer performance regressions
with the current wake_tx_queue implementation.
Therefore disable it unless it is really
beneficial with current codebase (which is when
firmware supports smart pull-push tx scheduling).

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>