ath10k: implement updating shared htt txq state

Firmware 10.4.3 onwards can support a pull-push Tx
model where it shares a Tx queue state with the
host.

The host updates the DMA region it pointed to
during HTT setup whenever number of software
queued from (on host) changes. Based on this
information firmware issues fetch requests to the
host telling the host how many frames from a list
of given stations/tids should be submitted to the
firmware.

The code won't be called because not all
appropriate HTT events are processed yet.

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