ath10k: make some wmi functions public

Some functions can be shared across different WMI
ABIs. Make them public so different WMI backends
can use them from different source files in the
future.

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