ath10k: export htc tx rx handlers

Export HTC layer tx and rx handlers. This will be used by HIF layer
for per-CE data processing. Instead of callback mechanism, HIF will
call appropriate upper layers API directly.

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