ath10k: split ath10k_wmi_service_ready_event_rx

Since the both firmwares we are going to support,
have significantly different APIs (WMI and shared
structures), it's easier to actually split the whole
event handling functions, instead cutting them inside.

The fork starts now on ath10k_wmi_process_rx().

Signed-off-by: Bartosz Markowski <bartosz.markowski@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>