ath6kl: add support for ar6004 hw3.0

This change enables ath6kl driver to support ar6004 hw3.0. At the same time do
some fixes in firmware initialisation which applies to ar6004 hw1.3 as well.

Signed-off-by: Jessica Wu <wjessica@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>