ath10k: enable 10.x firmware branch support

Since the WMI API has been added and we can detect from the
FW IEs what firmware variant we deal with, turn on support
for 10.x firmware branch in ath10k_wmi_attach().

kvalo: improve the commit log

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