ath6kl: AR6004 SDIO support

Add support for AR6004 SDIO. Tested scan, association (open mode) and
ping.

kvalo: change commit log a bit, drop board address changes

Signed-off-by: Naveen Gangadharan <ngangadh@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>