ath10k: implement basic support for new tx path firmware

This allows to use the new firmware which
implements the new tx data path. Without this
patch firmware supporting new tx path stops
responding shortly after booting.

This patch doesn't implement the entire pull-push
logic available in the new firmware. This will be
done in subsequent patches.

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