ath10k: deduplicate wmi service ready logic

The logic responsible for processing the event is
no different across different firmware binaries.
The difference that needs to be dealt with is the
ABI of data structures.

The intermediate structure uses __le32 to avoid
extra memory allocations to byteswap
variable-length substructures (i.e. host mem
chunks).

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